Wetlands and Urbanization: Implications for the Future

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Wetlands and Urbanization Implications for the Future

Wetlands and Urbanization Implications for the Future Edited by

Amanda L. Azous Environmental Scientist Azous Environmental Sciences

Richard R. Horner

Water Resources Consultant Research Associate Professor Landscape Architecture and Civil and Environmental Engineering University of Washington, Seattle

LEWIS PUBLISHERS Boca Raton London New York Washington, D.C.

L1386/frame/FM Page 4 Thursday, July 13, 2000 9:25 AM

Library of Congress Cataloging-in-Publication Data Wetlands and urbanization : implications for the future / edited by Amanda L. Azous and Richard R. Horner. p. cm. Includes bibliographical references and index. ISBN 1-56670-386-7 1. Wetland ecology—Washington (State)—Puget Sound Region. 2. Wetland management—Washington (State)—Puget Sound Region. 3. Wetlands—Washington (State)—Puget Sound Region. 4. Urbanization—Washington (State)—Puget Sound Region. I. Azous, Amanda L. II. Horner, Richard R. (Richard Ray) QH105.W2 W38 2000 577.68′09797′7—dc21

00-032730 CIP

This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. All rights reserved. Authorization to photocopy items for internal or personal use, or the personal or internal use of specific clients, may be granted by CRC Press LLC, provided that $.50 per page photocopied is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA. The fee code for users of the Transactional Reporting Service is ISBN 1-56670-386-7-/009/$0.00+$.50. The fee is subject to change without notice. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from CRC Press LLC for such copying. Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. The research described in this document has been funded by the U.S. Environmental Protection Agency and the Washington State Department of Ecology with funds obtained from the National Oceanic Atmospheric Administration, and appropriated for Section 306b of the Coastal Zone Management Act of 1972. King County Department of Natural Resources and Surface Water Management Division also funded this research. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. The views expressed herein are those of the authors and do not necessarily reflect the views of the publisher or any of the funding agencies.

© 2001 by CRC Press LLC Lewis Publishers is an imprint of CRC Press LLC No claim to original U.S. Government works International Standard Book Number 1-56670-386-7 Library of Congress Card Number 00-032730 Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Printed on acid-free paper


Preface In the early 1980s stormwater managers and developers were proposing to store urban runoff in wetlands to reduce flooding impacts and to protect stream channels from erosion. There was also interest in exploiting the known ability of wetlands to capture and retain pollutants in stormwater. In response to these proposals, natural resource managers argued that flood storage and pollutant trapping were only two of the numerous functions attributable to wetlands. Among other values were groundwater recharge and discharge, shoreline stabilization, food chain support, and habitat for wildlife. It was further claimed that using wetlands for stormwater management would likely damage these other vital functions. Both stormwater and natural resources managers came together in early 1986 in the Puget Sound area of Washington State to consider how best to resolve these national issues concerning wetlands and stormwater management. Together, representatives from federal, state, and local agencies; academic institutions; and other local interests determined information and management needs required to guide policy and management of wetlands. Out of these requests was born the design of a research program that would produce such information to guide policy and management of wetlands. The research was to identify the short- and long-term impacts of urban stormwater on palustrine wetlands; develop management criteria by wetland type; recommend stormwater management strategies that avoided or minimized negative effects on wetlands; and to identify features critical to improving urban runoff water quality prior to entering wetlands. Early in our studies, it became apparent that wetlands in urbanizing watersheds would inevitably be impacted by clearing, development, and other anthropogenic activities even if there was no intention to use them for stormwater management. We also learned it was essential to identify the characteristics of wetland watersheds and the surrounding landscapes in order to understand the relationships between urban stormwater discharge and wetland ecology. In this book you will learn what we found monitoring and analyzing the five major structural and ecological components of wetlands: hydrology, water quality, soils, plants, and animals in wetlands over an eight-year period. These pages provide a thorough descriptive ecology of studied wetlands, discussions of urbanization influences affecting these wetlands, and substantive recommendations for minimizing potential adverse stormwater impacts from urbanization. This information is developed from comparisons of wetlands located in watersheds undergoing urbanization to wetlands in watersheds remaining mostly undeveloped during our studies. Continued urbanization of the natural landscape is an ongoing ever-increasing activity, driving efforts to protect remaining wetlands. The goal of this book is to support protection efforts by increasing professional and public knowledge of wet-


land functions in urbanizing environments and to improve the management of both wetland resources and urban stormwater management. Puget Sound Wetlands and Stormwater Management Research Program Richard R. Horner Amanda L. Azous Klaus O. Richter Lorin E. Reinelt Sarah S. Cooke


About the Puget Sound Wetlands and Stormwater Management Program Team Amanda L. Azous is an environmental scientist, consultant, and sole proprietor of Azous Environmental Sciences, a private consulting firm established in Seattle, Washington in 1990 and located on Orcas Island, Washington since 1993. Ms. Azous received a Bachelor of landscape architecture and an M.S. in environmental engineering and science, from the University of Washington, Seattle and she is also a registered professional wetland scientist. Amanda Azous has worked on a broad range of projects including development of environmental policy, writing environmental protection regulations, and developing performance standards for wetland restoration and mitigation projects. Her recent experience includes wetland design, enhancement and restoration, watershed analysis, environmental impact assessment, water quality studies, GIS analysis of landscapes, land use surveys, and environmental impact evaluations. Her firm specializes in land management plans for wetlands, forestry, conservation, and stewardship as well as evaluations of environmental factors as a basis for community planning. She has authored and co-authored several journal articles and numerous technical reports addressing community planning, urban stormwater impacts, and management of biological communities in urbanizing watersheds. Richard R. Horner received his B.S. and M.S. degrees from the University of Pennsylvania and a Ph.D. in environmental engineering from the University of Washington in 1978. Following 13 years of college teaching and professional practice, he joined the University of Washington faculty in 1981. Since 1993 he has split his time between private consulting and teaching at the University of Washington, where he is a research associate professor with appointments in civil and environmental engineering, landscape architecture, and urban horticulture. Dr. Horner’s principal interests involve analyzing the effects of human activities, especially diffuse landscape sources of water pollution, on natural freshwater resources, and solutions that protect those resources. He founded the Center for Urban Water Resources Management at the University of Washington in 1990 to advance applied research and education in these areas, directed the center for three years, and continues as an affiliated faculty member. Dr. Horner coordinated the Puget Sound Wetlands and Stormwater Management Research Program, the basis for this book, from its beginning in 1986 to its conclusion in 1997. He has also been a principal investigator on more than 30 other research projects in his area of interest, funded by agencies such


as National Science Foundation, National Research Council, U.S. Environmental Protection Agency, the Washington State Departments of Ecology and Transportation, and a number of Puget Sound regional and local governments. His consulting clients have included many of these same agencies, the Natural Resources Defense Council, the Santa Monica and San Diego Baykeeper organizations, the Greater Vancouver (Canada) Regional District, and many of the national environmental consulting firms. Dr. Horner is the author or co-author of one previously published book and more than 50 refereed journal publications, book chapters, and papers in conference proceedings. His current University of Washington teaching includes a graduate watershed analysis and design studio in landscape architecture and a number of continuing education courses through engineering professional programs. Klaus O. Richter is the senior wetland ecologist in King County’s Department of Natural Resources. He received his B.S. in forestry/wildlife biology at the State University of New York (SUNY) College of Environmental Sciences and Forestry in Syracuse, an M.S. in science education at SUNY in Oswego, and a Ph.D. in forest zoology at the University of Washington, Seattle. For the past 15 years Dr. Richter has specialized in freshwater wetland science, management, protection, and regulation. As co-recipient of the 1996 National Wetlands Award in Science Research sponsored by the Environmental Law Institute and the EPA, he was honored for his research of amphibian ecology and reproduction in urban areas. His models to account for amphibian declines in urbanizing landscapes are being applied to reduce amphibian losses through improved stormwater management and in implementing site-specific wetland enhancement, restoration and creation practices throughout the Puget Sound and the U.S. Dr. Richter has authored numerous papers on the monitoring, distribution, and decline of amphibians as well as habitat mitigation criteria. Additionally, he helped develop Washington State’s Hydrogeomorphic Wetlands Functional Assessment and is currently developing methods and metrics (i.e., biocriteria) applicable to employing amphibians as bioindicators of wetland/watershed condition for EPA’s Wetland Division in Washington, D.C. Dr. Richter is also a popular instructor at local universities and colleges and leads numerous training courses on wetland monitoring, management, and restoration. Lorin E. Reinelt is a Senior Water Resources Engineer for the Public Works Engineering Department at the City of Issaquah. He is responsible for stormwater capital projects, including stream rehabilitation projects for flood mitigation and habitat enhancement, water quality treatment, and local drainage control. He also works in a regional role as the Sammamish watershed coordinator, supporting the Sammamish Watershed Forum, and implementing fish habitat, water quality, and flood protection projects. Dr. Reinelt has been involved in public service, research, education, and consulting on water resource issues for the past 15 years. This includes nonpoint source pollution management, wetlands and stormwater management, basin planning, aquatic resource monitoring, flood hazard mitigation, water quality assessment, and


groundwater management. Previously, he was employed by the King County Surface Water Management Division, the Center for Urban Water Resources Management at the University of Washington, and in private consulting. Dr. Reinelt has a B.S. in civil engineering from the University of the Pacific, a M.S. in environmental engineering and science from the University of Washington, and a Ph.D. in water and environmental studies from Linköping University in Sweden. He is a registered professional wetland scientist and engineer-in-training. Sarah S. Cooke, Ph.D. (edaphic ecology), M.S. (plant taxonomy), M.S. (geology, biology), is a registered professional wetland scientist, soils scientist (SS), and has a national reputation in wetlands and plant-soil interactions (geobotany) research. Dr. Cooke has 20 years experience in ecological and geological research, with 14 years in wetlands ecological research and environmental consulting in the Pacific Northwest. She specializes in wetland restoration design and implementation and has conducted wetland inventories, delineations, baseline studies, monitoring programs, rare plant surveys, soil assessments, vegetation mapping, and watershed analysis in the Pacific Northwest. Dr. Cooke developed the Semi-Quantitative Assessment Methodology (SAM) functional assessment used by many wetlands professionals; she was on the development team for the Washington State Wetlands Functional Assessment Methodology. Her most recent publication was A Field Guide to the Common Wetland Plants of Western Washington and Northwestern Oregon (Seattle Audubon Society, 1997), the definitive guide to the region’s wetland plants. Dr. Cooke has taught assessment methodologies, wetlands science and ecology, delineation protocols, hydric soil science, and wetland plant identification at the University of Washington and Portland State University. She has provided expert training for agency personnel and private consultants in soils and botany throughout the Pacific Northwest.


Contributors Amanda L. Azous Azous Environmental Sciences P.O. Box 530 Olga, WA 98279

Sarah Spear Cooke, Ph.D. Cooke Scientific Services, Inc. 4231 N.E. 110th St Seattle, WA 98125

Richard R. Horner, Ph.D. Civil and Environmental Engineering and Landscape Architecture Department University of Washington Seattle, WA 98195

Marion Valentine U.S. Army Corps of Engineers 4673 East Marginal Way South Seattle, WA 98134

Klaus O. Richter, Ph.D. King County Department of Natural Resources Water and Land Resources Division 201 S. Jackson Street Suite 600 Seattle, WA 98104 Lorin E. Reinelt, Ph.D. King County Department of Natural Resources 201 S. Jackson Street, Suite 600 Seattle, WA 98104

Ken A. Ludwa Parametrix, Inc. 5808 Lake Washington Boulevard N.E. Kirkland, WA 98033 Brian L. Taylor Entranco Engineers 10900 NE 8th Street, Suite 300 Bellevue, WA 98004 Nancy T. Chinn Montgomery Water Group P.O. Box 2517 Kirkland, WA 98083

Jeff Burkey King County Department of Natural Resources 201 S. Jackson Street, Suite 600 Seattle, WA 98104


Acknowledgments The editors thank co author and fellow scientist Dr. Klaus Richter for his commitment to wetland science and unending dedication to producing this book. The resulting publication has been significantly enhanced thanks to his efforts. The authors would like to thank the many individuals who contributed to this research effort. This project would not have been possible without the help of Dr. Derek Poon who understood the importance of developing environmental policy and regulations based on science and proved it by consistently finding funding for this research. We gratefully acknowledge his contribution to the on-going success of our efforts. We would especially like to thank Erik Stockdale who was one of the visionaries behind the Puget Sound Wetlands and Stormwater Research Program and a major contributor to our early studies. Our thanks to Dr. Kern Ewing for his continuing dedication and thoughtful contributions to this work. We also want to acknowledge Dr. Fred Weinmann for his many helpful comments and unending support. Our technical advisory committee members are too numerous to mention but we owe each of them great thanks for the direction and institutional support they provided. Our heartfelt thanks also to Tina Rose, graphic designer, who capably produced many of the technical illustrations used for this publication. Finally, we appreciate the hard work of many graduate students who gathered data and contributed important research, some of whom we may not have adequately acknowledged in individual chapters, but to whom we are indebted. The research that serves as the basis for the chapters in this book was made possible by the organizations that funded and supported this long-term study. Our thanks to: Washington State Department of Ecology U.S. Environmental Protection Agency, Region 10 King County Department of Development and Environmental Services King County Department of Natural Resources King County Surface Water Management Division University of Washington


Table of Contents Section I: Overview of the Puget Sound Wetlands and Stormwater Management Research Program Introduction................................................................................................................3 Richard R. Horner Section II: Descriptive Ecology of Freshwater Wetlands in the Central Puget Sound Basin Chapter 1 Morphology and Hydrology....................................................................................31 Lorin E. Reinelt, Brian L. Taylor, and Richard R. Horner Chapter 2 Water Quality and Soils...........................................................................................47 Richard R. Horner, Sarah S. Cooke, Lorin E. Reinelt, Kenneth A. Ludwa, and Nancy T. Chin Chapter 3 Characterization of Central Puget Sound Basin Palustrine Wetland Vegetation ................................................................................................................69 Sarah S. Cooke and Amanda L. Azous Chapter 4 Macroinvertebrate Distribution, Abundance, and Habitat Use ...............................97 Klaus O. Richter Chapter 5 Amphibian Distribution, Abundance, and Habitat Use ........................................143 Klaus O. Richter and Amanda L. Azous Chapter 6 Bird Distribution, Abundance, and Habitat Use ...................................................167 Klaus O. Richter and Amanda L. Azous Chapter 7 Terrestrial Small Mammal Distribution, Abundance, and Habitat Use................201 Klaus O. Richter and Amanda L. Azous


Section III: Functional Aspects of Freshwater Wetlands in the Central Puget Sound Basin Chapter 8 Effects of Watershed Development on Hydrology ...............................................221 Lorin E. Reinelt and Brian L. Taylor Chapter 9 Effects of Watershed Development on Water Quality and Soils..........................237 Richard R. Horner, Sarah S. Cooke, Lorin E. Reinelt, Kenneth A. Ludwa, Nancy T. Chin, and Marian Valentine Chapter 10 Wetland Plant Communities in Relation to Watershed Development ..................255 Amanda L. Azous and Sarah S. Cooke Chapter 11 Emergent Macroinvertebrate Communities in Relation to Watershed Development ..........................................................................................................265 Kenneth A. Ludwa and Klaus O. Richter Chapter 12 Bird Communities in Relation to Watershed Development..................................275 Klaus O. Richter and Amanda L. Azous Section IV: Management of Freshwater Wetlands in the Central Puget Sound Basin Chapter 13 Managing Wetland Hydroperiod: Issues and Concerns........................................287 Amanda L. Azous, Lorin E. Reinelt, and Jeff Burkey Chapter 14 Wetlands and Stormwater Management Guidelines .............................................299 Richard R. Horner, Amanda L. Azous, Klaus O. Richter, Sarah S. Cooke, Lorin E. Reinelt, and Kern Ewing Index ......................................................................................................................325

Section I Overview of the Puget Sound Wetlands and Stormwater Management Research Program

Introduction Richard R. Horner CONTENTS The Issues ..................................................................................................................4 Potential Impacts of Urbanization on Wetlands .......................................................5 Sources of Impacts to Wetlands ................................................................................6 Influence of Wetland and Watershed Characteristics on Impacts to Wetlands.....................................................................................................................6 Hydrologic Impacts ...................................................................................................7 Water Quality Impacts...............................................................................................7 Direct Water Quality Impacts...........................................................................7 Hydrologic Impacts on Water Quality .............................................................8 Impacts to Wetland Soils...........................................................................................8 Hydrologic Impacts to Wetland Soils ..............................................................8 Water Quality Impacts to Wetland Soils..........................................................8 Impacts to Vegetation ................................................................................................9 Hydrologic Impacts on Vegetation ...................................................................9 Water Quality Impacts on Vegetation.............................................................10 Impacts to Wetland Fauna .......................................................................................11 Hydrologic Impacts on Wetland Fauna..........................................................11 Water Quality Impacts on Wetland Fauna .....................................................12 Use of Wetlands for Stormwater Treatment............................................................13 Puget Sound Wetlands and Stormwater Management Research Program13 Design ......................................................................................................................13 Literature Review and Management Needs Survey................................................13 Research Program Design .......................................................................................14 Wetlands Impacted by Urbanization in the Puget Sound Basin.............................14 Stormwater Impact Studies......................................................................................15 Definition of Watershed and Surrounding Landscape Characteristics ...................20 Organization of the Monograph ..............................................................................21 References................................................................................................................21

The Puget Sound Wetlands and Stormwater Management Research Program (PSWSMRP) was a regional research effort intended to define the impacts of urbanization on wetlands. The wetlands chosen for the study were representative of those found in the Puget Sound lowlands and most likely to be impacted by urban devel1-56670-386-7/01/$0.00+$.50 © 2001 by CRC Press LLC

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Wetlands and Urbanization: Implications for the Future

opment. The program’s goal was to employ the research results to improve the management of both urban wetland resources and stormwater. This overview section begins by defining the issues facing the program at its inception. It then summarizes the state of knowledge on these issues existing at the beginning and in the early stages of the program. It concludes by outlining the general experimental design of the study. Subsequent sections present the specific methods used in the various monitoring activities.

THE ISSUES The program was inspired by proposals of stormwater managers and developers in the 1980s to store urban runoff in wetlands to prevent flooding and to protect stream channels from the erosive effects of high peak flow rates.1,2 Stormwater managers were also interested in exploiting the known ability of wetlands to capture and to retain pollutants in stormwater, interrupting their transport to downstream water bodies (see listed citations for discussion of the use of wetlands for runoff quality control).1-6 In response to proposals to use wetlands for urban runoff storage, natural resources managers argued that flood storage and pollutant trapping are only two of the numerous ecological and social functions filled by wetlands. Among the other values of wetlands are groundwater recharge and discharge; shoreline stabilization; and food chain, habitat, and other ecological support for fish, waterfowl, and other species.7,8 Resource managers further contended that using wetlands for stormwater management could damage other important wetland functions.6,9-12 They noted the general lack of information on the types and extent of impacts to wetlands used for stormwater treatment.3,10-13 Several researchers have suggested that findings about the impacts of municipal wastewater treatment in wetlands are relevant to stormwater treatment in wetlands.3,14 In some cases, wastewater treatment in wetlands has caused severe ecological disruptions, particularly when wastewater delivery is uncontrolled.15,16 A number of studies have raised concerns about possible long-term toxic metal accumulations, biomagnification of toxics in food chains, nutrient toxicity, adverse ecological changes, public health problems, and other impacts resulting from wastewater treatment in wetlands.17-20 Other researchers have reported negative impacts on wetland ecosystems from wastewater treatment. Wastewater additions can lead to reduced species diversity and stability, and a shift to simpler food chains.21,22 Wastewater treatment in natural northern wetlands tended to promote the dominance of cattails (Typha spp.).23 In addition, animal species diversity usually declined. Discharge of wastewater to a bog and marsh wetland eliminated spruce and promoted cattails in both the bog and marsh portions.24 Thirty years of effluent discharge to a peat bog caused parts of the bog to become a monoculture cattail marsh.25 Application of chlorinated wastewater to a freshwater tidal marsh reduced the diversity of annual plant species.26 These findings on the effects of wastewater applications to wetlands have probable implications for the use of wetlands for stormwater treatment.

Introduction

5

Despite the controversy over use of natural wetlands for stormwater treatment, it became apparent in early discussions on the subject that wetlands in urbanizing watersheds will inevitably be impacted by urbanization, even if there is no intention to use them for stormwater management. For example, the authors of a U.S. Environmental Protection Agency (USEPA) handbook on use of freshwater wetlands for stormwater management stated that the handbook was not intended to be a statement of general policy favoring the use of wetlands for runoff management, but acknowledged that some 400 communities in the Southeast were already using wetlands for this purpose.15 Moreover, directing urban runoff away from wetlands in an effort to protect them can actually harm them. Such efforts could deprive wetlands of necessary water supplies, changing their hydrology and threatening their continued existence as wetlands.2 In addition, where a wetland’s soil substrate is subsiding, continuous sediment inputs are necessary to preserve the wetland in its current condition.27 Directing runoff to wetlands can help to furnish nutrients that support wetland productivity.2 In its early years, the program focused on evaluating the feasibility of incorporating wetlands into urban runoff management schemes. Given this objective, the researchers initially viewed the issues more from an engineering perspective rather than natural science. However, in later years, an appreciation of the fact that urban runoff reaches wetlands, whether intended or not, led the researchers to shift their inquiry to more fundamental questions about the impact of urbanization on wetlands. Thereafter, the program’s point of view ultimately merged natural science and engineering considerations. The information yielded by the program will, therefore, be useful to wetland and other scientists, as well as to stormwater managers.

IMPACTS OF URBANIZATION ON WETLANDS Urbanization impacts wetlands in numerous direct and indirect ways. For example, construction reportedly impacts wetlands by causing direct habitat loss, suspended solids additions, hydrologic changes, and altered water quality.28 Indirect impacts, including changes in hydrology, eutrophication, and sedimentation, can substantially alter wetlands in addition to direct impacts, such as drainage and filling.29 Urbanization may affect wetlands on the landscape level, through loss of extensive areas, at the wetland complex level, through drainage or modification of some of the units in a group of closely spaced wetlands, and at the level of the individual wetland, through modification or fragmentation.30 Over the past several decades, it has become increasingly apparent that untreated runoff is a significant threat to the country’s water quality. There has, consequently, been substantial research about the relationship between urbanization and runoff quality and quantity. However, this program focused on the impacts of runoff to wetlands themselves, and not on the effects of urbanization on runoff flowing to wetlands. Runoff can alter four major wetland components: hydrology, water quality, soils, and biological resources.31,32 Because impacts to individual wetland components affect the condition of others, it is difficult to distinguish between the effects of each

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impact or to predict the ultimate condition of a wetland component by simply aggregating the effects of individual impacts.31,33 Moreover, processes within wetlands interact in complex ways. For example, wetland chemical, physical, and biological processes interact to influence the retention, transformation, and release of a large variety of substances in wetlands. Increased peak flows transport more sediment to wetlands that, in turn, may alter the wetlands’ vegetation communities and impact animal species dependent on the vegetation.

SOURCES OF IMPACTS TO WETLANDS Brief consideration of how urbanization affects runoff illustrates the potential for dramatic alteration of wetlands. Hydrologic change is the most visible impact of urbanization. Hydrology concerns the quantity, duration, rates, frequency, and other properties of water flow. It has been called the linchpin of wetland conditions because of its central role in maintaining specific wetland types and processes.34,35 Moreover, impacts on water quality and other wetland components, to a considerable degree, are a function of hydrologic changes.36 Of all land uses, urbanization has the greatest ability to alter hydrology. Urbanization typically increases runoff peak flows and total flow volumes and damages water quality and aesthetic values. For example, one study comparing a rural and an urban stream found that the urban stream had a more rapidly rising and falling hydrograph, and exhibited greater bed scouring and suspended solids concentrations.37 Pollutants reach wetlands mainly through runoff.38,39 Urbanized watersheds generate large amounts of pollutants, including eroded soil from construction sites, toxic metals and petroleum wastes from roadways and industrial and commercial areas, and nutrients and bacteria from residential areas. By volume, sediment is the most important nonpoint pollutant.39 At the same time that urbanization produces larger quantities of pollutants, it reduces water infiltration capacity, yielding more surface runoff. Pollutants from urban land uses, therefore, are more vulnerable to transport by surface runoff than pollutants from other land uses. Increased surface runoff combined with disturbed soils can accelerate the scouring of sediments and the transport and deposition of sediments in wetlands.11,40 Thus, there is an intimate connection between runoff pollution and hydrology.

INFLUENCE OF WETLAND AND WATERSHED CHARACTERISTICS ON IMPACTS TO WETLANDS Watershed and wetland characteristics both influence how urbanization affects wetlands. For example, impacts of highways on wetlands are affected by such factors as highway location and design, watershed vulnerability to erosion, wetland flushing capacity, basin morphology, sensitivity of wetland biota, and wetland recovery capacity.41 Regional storm patterns also have a significant influence on impacts to wetlands.31 Hydrologic impacts are affected by such factors as watershed land uses; wetland to watershed area ratios; and wetland soils, bathymetry, vegetation, and inlet and outlet conditions.31,42

Introduction

7

Clearly, an assessment of the impacts of urbanization on a wetland should take into account the landscape in which the wetland is located. Some have suggested that a landscape approach might be useful for evaluating the effect of cumulative impacts on a wetland’s water quality function.43 The rationale for such an approach is that most watersheds contain more than one wetland, and the influence of a particular wetland on water quality depends both on the types of the other wetlands present and their positions in the landscape.

HYDROLOGIC IMPACTS The direct impacts of hydrologic changes on wetlands are likely to be far more dramatic, especially over the short term, than other impacts. Hydrologic changes can have large and immediate effects on a wetland’s physical condition, including the depth, duration, and frequency of inundation of the wetland. It is fair to say that changes in hydrology caused by urbanization can exert complete control over a wetland’s existence and characteristics. One study, using the Surface Water Management Model (SWMM), predicted that urbanization bordering a swamp forest would increase runoff volumes by 4.2 times.44 Greater surface runoff is also likely to increase velocities of inflow to wetlands, which can disturb wetland biota and scour wetland substrates.39 Increased amounts of stormwater runoff in wetlands can alter water level response times, depths, and duration of water detention.31 Reduction of watershed infiltration capacity is likely to cause wetland water depths to rise more rapidly following storm events. Diminished infiltration in wetland watersheds can also reduce stream baseflows and groundwater supplies to wetlands, lengthening dry periods and impacting species dependent on the water column.15,45

WATER QUALITY IMPACTS DIRECT WATER QUALITY IMPACTS Prior to the PSWSMRP study, there was very little information specifically covering the impacts of urban runoff on water quality within wetlands.39 On the other hand, there have been extensive inquiries into the effects of urbanization on runoff and receiving water quality generally.122 Much of this information undoubtedly is suggestive of the probable effects of urban runoff on wetland water quality. There have also been numerous “before and after” studies evaluating the effectiveness of wetlands for treatment of municipal wastewater and urban runoff.3,4,10,12,20,46-51 Many of these studies have focused on the effectiveness of wetlands for water treatment rather than on the potential for such schemes to harm wetland water quality. Nevertheless, data on the quality of inflow to and pollutant retention by wetlands are likely to give some indication of the effects of urban runoff on wetland water quality. Studies on the effects of wastewater and runoff on other wetland components, such as vegetation, also may provide indirect evidence of impacts on wetland water quality.22,24-26,52-57 A number of researchers have warned of the risks of degradation of wetland water quality and other values from intentional routing of runoff through

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wetlands.3,10-12,14,58 Subsequent sections in this monograph describe the results of water quality impact studies performed by the program.

HYDROLOGIC IMPACTS

ON

WATER QUALITY

Hydrology influences how water quality changes will impact wetlands. Hydrologic changes can make a wetland more vulnerable to pollution.59 Increased water depths or frequencies of flooding can distribute pollutants more widely through a wetland.39 How wetlands retain sediment is directly related to flow characteristics, including degree and pattern of channelization, flow velocities, and storm surges.10 Toxic materials can accumulate more readily in quiescent wetlands.60 A study on use of wetlands for stormwater treatment found that wetlands with a sheet flow pattern retained more phosphorus, nitrogen, suspended solids, and organic carbon than channelized systems, which were found to be ineffective.50 Changes in hydroperiod can also affect nutrient transformations and availability and the deposition and flux of organic materials.36,61 One study observed higher phosphorus concentrations in stagnant than in flowing water.62 In wetland soils, the advent of anaerobic conditions can transform phosphorus to dissolved forms.31 Another study reported that anaerobic conditions in flooded emergent wetlands increased nutrient availability to wetland plants, compared to infrequently flooded sites.63

IMPACTS TO WETLAND SOILS HYDROLOGIC IMPACTS

TO

WETLAND SOILS

Flow characteristics within wetlands directly influence the rate and degree of sedimentation of solids imported by runoff.22 If unchecked, excessive sedimentation can alter wetland topography and soils, and, ultimately result in the filling of wetlands. Alternatively, elevated flows can scour a wetland’s substrate, changing soil composition, and leading to a more channelized flow.40 Materials accumulated over several hundred years could, therefore, be lost in a matter of decades.64

WATER QUALITY IMPACTS

TO

WETLAND SOILS

The physical, chemical, and biological characteristics of wetland soils change as they are subjected to urban runoff.31 The physical effects of runoff on wetland soils, including changes in texture, particle size distributions, and degree of saturation are not well documented.31 However, a wetland’s soil can be expected to acquire the physical characteristics of the sediments retained by the wetland. Suspended matter has a strong tendency to absorb and adsorb other pollutants.39 Sedimentation, therefore, is a major mechanism of pollutant removal in wetlands.3,14 Chemical property changes in wetland soils typically reflect sedimentation patterns.65,66 Materials are often absorbed by wetland soils after entering a wetland, as well.67 When nutrient inputs to wetlands rise, temporary or long-term storage of nutrients in ecosystem components, including soils, can increase.23 Rates of nutrient transfer among ecosystem components and flow through the system may also accelerate. When chlorinated wastewater was sprayed onto a freshwater tidal marsh,

Introduction

9

surface litter accumulated nitrogen and phosphorus.26 However, although wetland soils can retain nutrients, a change of conditions, such as the advent of anaerobiosis and changed redox potential, can transform stored pollutants from solid to dissolved forms, facilitating export from the soil.31 The capacity of wetland soils to retain phosphorus becomes saturated over time.68-70 If the soil becomes saturated with phosphorus, release is likely. Wetland soils can also trap toxic materials, such as metals.31 High toxic metals accumulations have been found in inlet zones of wetlands affected by urban runoff.71 One study observed increased sediment metals concentrations in several locations in a wetland receiving wastewater.56 The quantity of metals that a wetland can absorb without damage depends on the rate of metals accretion and degree of burial.15 If stormwater runoff alters soil pH and redox potential, many stored toxic materials can become immediately available to biota.72 Water quality impacts on wetland soils can eventually threaten a wetland’s existence. Where sediment inputs exceed rates of sediment export and soil consolidation, a wetland will gradually become filled. Filling by sediment is a particular concern for wetlands in urbanizing areas.39 Many wetlands have an ability to retain large amounts of sediment. For example, it was reported that a wetland captured 94% of suspended solids from stormwater.4 Other scientists observed that a stormwater treatment wetland lost 18% of permanent storage volume and 5% of total storage volume because of high rates of solids retention.51

IMPACTS TO VEGETATION Impacts on wetland hydrology and water quality can, in turn, affect wetland vegetation. Emergent zones in Pacific Northwest wetlands receiving urban runoff are dominated by an opportunistic grass species, Phalaris arundinacea, while nonimpacted wetlands contain more diverse groupings of species.73 Marked changes in community structure, vegetation dynamics, and plant tissue element concentrations were observed in New Jersey Pine Barrens swamps receiving direct storm sewer inputs, compared to swamps receiving less direct runoff.53 However, human impacts on wetland ecosystems can be quite subtle. For example, upon reconsidering data from two prior studies of ecological changes in wetlands, one inquiry concluded that human influences, and not natural succession, as originally believed, were the principal causes of change in the vegetation of two New England wetlands.29

HYDROLOGIC IMPACTS

ON

VEGETATION

Hydrologic changes can have significant impacts on the livelihood of the whole range of wetland flora, from bacteria to the higher plants. It was observed that microbial activity in wetland soils correlated directly to soil moisture.47 However, surface microbial activity decreased when soils were submerged and became anaerobic.4 To a greater or lesser degree, wetland plants are also adapted to specific hydrologic regimes. For example, the frequency and duration of flooding was documented to have determined the distribution of bottomland tree species.74 Flood plain terraces with different flooding characteristics had distinct species composi-

10


tions. Increased watershed imperviousness can cause faster runoff velocities during storms that can impact wetland biota.39 However, as watersheds become more impervious, stream base flows and groundwater supplies can decline. As a result, dry periods in wetlands may become prolonged, impacting species dependent on the inundation.15,45 Changes in average depths, duration, and frequency of inundation ultimately can alter the species composition of plant and animal communities.39 There have been numerous reports on the tolerance to flooding of wetland and non-wetland trees and plants.75-94 While flooding can harm some wetland plant species, it promotes others.31 There is little information available on the impacts of hydrologic changes on emergent wetland plants, although some species that can tolerate extended dry periods have been identified.95 Hay yields in native wet meadows were reported to have increased with the length of flood irrigation if depths remained at 13 cm or less, and declined if depths stayed at 19 cm for 50 days or longer.78 Plant species often have specific germination requirements, and many are sensitive to flooding once established.96 The life stage of plant species is an important determinant of their flood tolerances. While mature trees of certain species may survive flooding, the establishment of saplings could be retarded.39 Where water levels are constantly high, wetland species may have a limited ability to migrate, and may be able to spread only through clonal processes because of seed bank dynamics.97 The result may be reduced plant diversity in a wetland. However, anaerobic conditions can increase the availability of nutrients to wetland plants.63 Hydrologic impacts on individual plant species eventually translate into long-term alterations of plant communities.15 Changes in hydroperiod can cause shifts in species composition, primary productivity, and richness.15,72 It has been theorized that changes in hydroperiod were among the causes of a decline of indigenous plant species and an increase in exotic species in New Jersey Pine Barrens cedar swamps.53 Early results of the PSWSMRP study indicated that wetlands with hydroperiods that fluctuated significantly between monthly high and low water levels have lower species richness than systems with lower monthly changes in water level.45,100 (See Chapter 10, Wetland Plant Communities in Relation to Watershed Development, for the results of the PSWSMRP study on the effects of water level changes on wetland vegetation.) In general, periodic inundation yields more plant diversity than either constantly wet or dry conditions.98,99 Monitoring in a Cannon Beach, Oregon wastewater treatment wetland revealed little change in herbaceous and shrub plant cover after two years of operation, except in channelized and deeply flooded portions, where herbaceous cover decreased.46 Slough sedge cover increased slightly in a shallowly flooded area. In 1986, flooding stress was observed in red alder trees in deeper parts of the wetland. In another wetland, part of which was drained and part of which was impounded to a greater depth, vegetation in the drained portion became more dense and diverse, but there was a marked decline in the number of species in the flooded portion after three years.93


ON

VEGETATION

High suspended solids inputs can reduce light penetration, dissolved oxygen, and overall wetland productivity.39 Inflow containing high concentrations of nutrients

Introduction

11

can also promote plant growth. One study reported, for example, that in a wastewater treatment wetland, plants closer to the discharge point had greater biomass and higher concentrations of phosphorus in their tissues, and the cattails were taller.57 When nutrient inputs to wetlands increase, they may be stored either temporarily or over the long-term in ecosystem components, including vegetation.101 Rates of nutrient movement, by transfer among ecosystems components and through the system, may accelerate as a result. Toxic materials in runoff can interfere with the biological processes of wetland plants, resulting in impaired growth, mortality, and changes in plant communities. The amount of metals absorbed by plants, for some species, is a function of supply. In cedar swamps in the New Jersey Pine Barrens, plants took up more lead when direct storm sewer inputs were present than when runoff was less direct.53 The degree to which plants bioaccumulate metals is highly variable. Pickleweed (Salicornia sp.) was found to concentrate metals, especially zinc and cadmium, more than mixed marsh and upland grass vegetation.52 However, plants in a brackish marsh that had received stormwater runoff for more than 20 years did not appear to concentrate copper, cadmium, lead, and zinc any more than plants in control wetlands not receiving storm water.3 While toxic metals accumulate in certain species, such as cattails, without causing harm, they interfere with the metabolism of other species.39 Toxic metals can harm certain species by interfering with nitrogen fixation.102 Metals can also impinge on photosynthesis in aquatic plants, such as waterweed (Elodea spp.).103 Another study (1981) reported that roadway runoff containing toxic metals had an inhibitory effect on algae.104 A bioassay study of the effects of stormwater on algae showed that nutrients did not stimulate growth as much as predicted because of the presence of metals in the stormwater.105 The germination rates of wetland plants exposed to roadside snowmelt in several concentrations were found to vary inversely with the concentration of snowmelt.54 Pollution in wetlands may impact plant community composition the most. The major effect observed of residential and agricultural runoff with high pH and nitrate concentrations was to cause indigenous aquatic macrophytes of the New Jersey Pine Barrens to be replaced by non-native species.55 Marked changes in plant community structure and vegetation dynamics in Pine Barrens cedar swamps were also reported where direct storm sewer inputs were present.53 Wetland plants that were exposed to roadside snowmelt in several concentrations, showed differences in community biomass, species diversity, evenness, and richness after one month of growth that varied inversely with snowmelt concentration.54 Impacts were not as severe where runoff was less direct.

IMPACTS TO WETLAND FAUNA HYDROLOGIC IMPACTS

ON

WETLAND FAUNA

Hydrologic changes also greatly affect wetland animal communities. In two coastal marshes, animal species richness and abundance declined as hydrologic disturbance increased.106 Shifts in plant communities as a result of hydrologic changes

12


can have impacts on the preferred food supply and cover of such animals as waterfowl. Increased imperviousness in wetland watersheds can reduce stream base flows and groundwater supplies, prolonging dry periods in wetlands and impacting species dependent on the water column. Many amphibians require standing water for breeding, development, and larval growth. Amphibians and reptile communities may experience changes in breeding patterns and species composition with changed water levels.107 Because amphibians place their eggs in the water column, the eggs may be directly damaged by changes in water depth. Alterations in hydroperiod can be especially harmful to amphibian egg and larval development if water levels decline and eggs attached to emergent vegetation are exposed and desiccated.108 Water temperature changes that accompany shifting hydrology may also impact egg development.109 Hydrologic changes have implications for other wetland animals, as well. Alterations to water quality and wetland soils caused by hydrologic changes may negatively affect animal species. For example, increased peak flows that accelerate sedimentation in wetlands or cause scouring can damage fish habitat.11 Mortality of the eggs and young of waterfowl during nesting periods may rise if water depths become excessive.31 Water level fluctuations resulting from an artificial impoundment in eastern Washington State caused a redistribution of bird populations. When potholes were flooded by the impoundment, waterfowl production was reduced, and breeding waterfowl were forced into the remaining smaller potholes.110 Hydrologic changes may impact mammal populations in wetlands by diminishing vegetative habitat and by increasing the potential for proliferation of disease organisms and parasites as base flows become shallower and warmer.108 Also, research has indicated a need to maintain habitat around wetlands that are receiving stormwater in order to permit free movement of animals during storm events.31


TO

WETLAND FAUNA

Pollutants can have both direct and indirect effects on wetland fauna. Road runoff containing toxic metals had an inhibitory effect on zooplankton, in addition to algae.104 A significant negative correlation between water conductivity (a general indicator of dissolved substance concentrations) and amphibian species richness was reported.45 Aquatic organisms, particularly amphibians, readily absorb chemical contaminants.111 Thus, the status of such organisms can be an effective indicator of a wetland’s health. The degree of bioaccumulation of metals in wetland animals varies by species. In a brackish marsh that had received storm runoff for 20 years, there was no observed bioaccumulation of metals in benthic invertebrates.112 However, a filter-feeding amphipod (Corophium sp.), known for its ability to store lead in an inert crystal form, accumulated significant amounts of lead. Water quality changes can indirectly harm fish and wildlife by reducing the coverage of plant species preferred for food and shelter.35,108,113 (Please see Section III for discussions of amphibian, emergent aquatic insect, bird, and small mammal communities in relation to watershed development and habitat conditions, and for the results of the program’s study on the effects of hydrologic and water quality changes on wetland animals.)

Introduction

13

USE OF WETLANDS FOR STORMWATER TREATMENT Impacts from intentional use of wetlands for stormwater management could be more harmful than those that would occur with incidental drainage from an urbanized watershed. For example, raising the outlet and controlling the outflow rate would, in general, change water depths and the pattern of rise and fall of water. Structural revisions to improve pollutant trapping ability would increase toxicant accumulations, in addition to the direct effects of construction. On the other hand, stormwater management actions could be linked with efforts to upgrade wetlands that are already highly damaged.

PUGET SOUND WETLANDS AND STORMWATER MANAGEMENT RESEARCH PROGRAM DESIGN Representatives of the stormwater and resource management communities in the Puget Sound area of Washington State formed a committee in early 1986 to consider how to best resolve questions concerning wetlands and stormwater runoff. Committee members came from federal, state, and local agencies, academic institutions, and other local interests. The Resource Planning Section of the government of King County, Washington coordinated the committee’s work. The committee’s initial effort was to enumerate the wetland resources that are implicated in urban stormwater management decisions and to identify the general types of effects that runoff could have on these resources. The committee members also oversaw the preparation of a literature review, designed to determine the extent to which previous work could address the issues before them, and a survey of management needs.

LITERATURE REVIEW AND MANAGEMENT NEEDS SURVEY The principal activity of the program’s first year was a comprehensive literature review, which concluded with a report and an annotated bibliography covering the reported research and observations relevant to the issue of stormwater and wetlands.114,115 The review was updated in 1991.39 These reviews concentrated on what was known and what was not known about these issues at the time. Best known was the performance of wetlands in capturing pollutants, mostly derived from studies on their ability to provide advanced treatment to municipal wastewater effluents. Only a small body of information pertained to stormwater. The greatest shortcoming of the literature concerned the ecological impacts to wetlands created by any kind of waste stream. The literature reviews also made clear the dearth of research on any aspect of Pacific Northwest wetlands, in contrast to some other areas of the country. Many detailed aspects of the subject of stormwater and wetlands were very poorly covered, including the relative roles of hydrologic and water quality modifications in stressing wetlands and the transport and fate of numerous toxicants in wetlands. On the basis of their discussions and the literature review, the committee members participated in a formal survey designed to identify the most important needs for

14


reaching the goal of protecting wetlands in urban and urbanizing areas, while improving the management of urban stormwater. The survey involved rating a long list of candidate management needs with respect to certain criteria. Computer processing of the ratings led to the following list of consensus high-priority management needs: • Definition of short- and long-term impacts of urban stormwater on palustrine wetlands; • Management criteria by wetland type; • Allowable runoff storage schedules that avoid or minimize negative effects on wetlands and their various functions; and • Features critical to urban runoff water quality improvement in wetlands.

RESEARCH PROGRAM DESIGN After completion of the literature review and management needs survey, the committee and staff assembled by King County turned to defining a research program to serve the identified needs. The program they developed included the following major components: • • • •

Wetland survey; Water quality improvement study; Stormwater impact studies; and Laboratory and special field studies.

The purpose of the wetland survey was to provide a broad picture of freshwater wetlands representative of those in the Puget Sound lowlands. The survey covered 73 wetlands throughout lowland areas of King County. One important goal of the survey was to identify how urban wetlands differ from those that are lightly affected by human activity. The survey’s design, results, and conclusions were published in previous reports.73,74 The survey results assisted in designing the remainder of the research program. The water quality improvement study was an intensive, two-year (1988–1990) effort to answer remaining questions about the water quality functioning of wetlands and is also discussed elsewhere.116 The results from the various portions of the program were used to develop extensive guidelines for coordinated management of urban wetlands and stormwater. These guidelines were continuously updated and refined as more information became available.

WETLANDS IMPACTED BY URBANIZATION IN THE PUGET SOUND BASIN The research program focused primarily on palustrine wetlands because urbanization in the Puget Sound region is impacting this wetland type more than other types. Palustrine wetlands are freshwater systems in headwater areas or isolated from other water bodies.117 They typically contain a combination of water and vegetation

Introduction

15

zones. Some palustrine wetlands consist of open water with only submerged or floating plants, or with no vegetation. Others include shallow or deep marsh zones containing herbaceous emergent plants, shrub-scrub vegetation, and sometimes forested plant communities. Two “poor fens” being impacted by urban development were also monitored during the study. Poor fens, commonly confused with true bogs, are a special wetland type that is of considerable interest in northern regions. Under natural conditions, water supply to poor fens consists only of precipitation and groundwater. The lack of surface water inflow restricts nutrient availability, resulting in a relatively unusual plant community adapted to low nutrition and the attendant acidic conditions. Such a community is vulnerable to increased nutrient supply and buffering by surface water additions.

STORMWATER IMPACT STUDIES The stormwater impact studies formed the core of the program. This field research was supplemented by the laboratory and special field studies, which allowed investigation of certain specific questions under more control than offered by the broader field studies. A special effort was made to ensure that research was conducted according to sound scientific design, so that the results and their application in management would be defensible. In order to approximate the classic “before and after, control and treatment” experimental design approach, the impact study included “control” and “treatment” wetlands. Nineteen wetlands were included in the stormwater impact study, with approximately half the treatment sites and the remainder of the control sites (general locations are shown in Figure 1). The treatment wetlands, located in areas undergoing urban development during the course of the study, were monitored before, during, and after urbanization. The goals of studying these wetlands were to characterize preexisting conditions and to assess the consequences of any changes accompanying urbanization and modification of stormwater inflow. The use of control sites was intended to make it possible to judge whether observed changes in treatment wetlands were the result of urbanization or of broader environmental conditions affecting all wetlands in the region. Control wetlands were paired with treatment sites on the basis of size, water and plant zone configuration, and vegetation habitat classifications. Not all of the treatment watersheds developed as much as anticipated at the outset of the study. Only six watersheds developed 10% or more than the developed area at the start of the study. Of these six, only three wetlands had significant increases in watershed development of 100, 73, and 42% with the remaining three having increases of only 10.5, 10.3, and 10.2%. Fortunately, watersheds of most of the control wetlands were characterized by relative stability in land use during the study. The unexpected slowness of development in the study watersheds affected our ability to identify differences between control and treatment pairs attributable to stormwater and urbanization. Also, the watersheds of control wetlands ranged from no urbanization to relatively high levels so no comparisons could be made unless the matched treatment wetland underwent significant urbanization in the watershed.

16


FIGURE 1 Puget Sound Wetlands and Stormwater Management Research Program study locations.

Under the circumstances, the plan to compare control and treatment pairs of wetlands was abandoned and revisions to the categories for data analyses were made. Several categories of wetlands related to land use and watershed changes were used in the program’s analyses and are shown in Table 1. Wetlands are identified as a control or a treatment wetland and land uses present in the watersheds of the wetlands at the start and completion of the study are listed. The table also lists watershed area, wetland area, and a categorization of wetland morphology. Because the program was interested in long-term as well as short-term effects, the monitoring of impacts was continued for eight years. Research in 1988 and 1989 generally provided the baseline data for the treatment wetlands. Data from 1990 reflected the early phase of urbanization in these wetlands. Monitoring resumed in 1993, shortly after a phase of building in the watersheds ended. Monitoring in 1995 was intended to document effects that took longer to appear.

47.35 183.73 38.45 69.20 27.11 54.63 357.34 359.36 296.64 198.22 183.32 45.73 3.24 84.58 64.35 3.64 193.04 88.22 11.74

0.81 1.98 2.10 1.74 2.02 3.84 7.28 1.62 12.55 6.09 7.69 2.23 0.61 1.50 10.52 1.62 2.83 10.12 2.06

OW FT OW OW OW FT FT OW FT FT FT FT OW OW OW FT OW OW OW

C C T T T C C C T C C C T T C C C C C

RC UC T T T UC UC RC T RC UC RC T T RC RC UC RC RC

N H L M M M M N M N H N H N N M M N N

13.3 74.7 10.5 88.8 23.9 56.6 81.2 1.5 54.7 12.8 69.8 4.1 0.0 23.5 2.4 12.5 77.8 0.0 0.0

13.3 75.2 52.7 87.9 34.4 56.6 81.2 1.5 64.9 11.0 73.8 4.1 100.0 34.0 2.4 12.5 78.2 0.0 0.0

0.0 0.5 42.2 –0.9c 10.5 0.0 0.0 0.0 10.2 –1.8 4.0 0.0 100.0 10.5 0.0 0.0 0.4 0.0 0.0

73.9 0.0 89.5 18.5 2.5 0.0 14.7 76.6 34.4 44.1 0.0 88.8 100.0 75.2 62.4 46.1 20.1 100.0 100.0

73.9 0.0 47.4 10.8 3.7 0.0 14.7 75.1 19.8 13.0 0.0 88.8 0.0 64.7 62.4 46.1 19.7 100.0 89.7

0.0 0.0 –42.1 –7.7 1.2 0.0 0.0 –1.5 –14.6 –31.1 0.0 0.0 –100.0 –10.5 0.0 0.0 –0.4 0.0 –10.3

4.1 54.9 3.4 24.6 5.1 19.9 30.8 3.6 20.0 5.8 21.8 2.9 2.0 5.1 3.4 11.8 18.5 2.0 2.0

4.1 55.4 10.6 24.2 10.6 19.9 30.8 3.6 20.6 6.1 21.6 2.9 40.0 6.8 3.4 11.8 17.0 2.0 2.3

Change

1995

1989

% Impervious Cover

Change

1995

1989

% Forest Cover

Change

1995

1989

Wetland Area (ha) Wetland Type OW = open water FT = flow through Treatment (T) or Control (C) Land Use Treatment and Controlsa Urbanization Categoryb

Watershed Area (ha)

Site AL3 B3I BBC24 ELS39 ELS61 ELW1 FC1 HC13 JC28 LCR93 LPS9 MGR36 NFIC12 PC12 RR5 SC4 SC84 SR24 TC13

% Urban Cover

Introduction

TABLE 1 Landscape Data for Study Wetlands

0.0 0.5 7.2 –0.4 5.5 0.0 0.0 0.0 0.6 0.3 –0.2 0.0 38.0 1.7 0.0 0.0 –1.5 0.0 0.3

a

17

RC = rural control (less than 12% impervious area and greater than 40% forest); UC = urban control (greater than 12% impervious area and less than 40% forest); T = treatment (wetlands that changed during the study period). b Column represents watershed urbanization at start of study: N = less than 4% impervious area and greater than 40% forest; H = greater than 20% impervious area and less than 7% forest; M = watershed conditions intermediate between N and H. c The watershed of ELS39 was estimated to be 15% developed in 1988 when the study began. The watershed was developed prior to the GIS analysis of 1989 and no accurate cover data is available until 1995.

18


Habitat Development

Watershed Conditions Wetland Community Structure

Wetland Morphology

Biological Responses

Descriptives linkages, conceptual models, quantitative algorithms

FIGURE 2 Puget Sound Wetlands and Stormwater Management Research Program experimental strategy.

Figure 2 illustrates the conceptual framework of the designs of the specific sampling programs pursued in the stormwater impact study to analyze and interpret the resulting data. The two blocks on the left of the diagram represent the driving forces determining a wetland’s character (Watershed Conditions and Wetland Morphology). The term “surrounding landscape” signifies that not only a wetland’s watershed (the area that is hydrologically contributory to the wetland) but also adjacent land outside of its watershed can influence the wetland. The surroundings include the wetland buffer, corridors for wildlife passage, and upland areas that provide for the needs of some wetland animals. Wetland morphology refers to form and structure and embraces shape, dimensions, topography, inlet and outlet configurations, and water pooling and flow patterns. The central block (Wetland Community Structure) represents the physical and chemical conditions that develop within a wetland and constitute a basis for its structure. Included are both quantity and quality aspects of its water supply and its soil system. Together, these structural elements develop various habitats that can provide for living organisms, represented by the block at the upper right of the diagram. Biota will respond depending on habitat attributes, as illustrated by the block at the lower right. It is a fundamental goal of the Puget Sound Wetlands and Stormwater Management Research Program to describe these system components for the representative wetlands individually and collectively. Connecting lines and arrows on Figure 2 depict the interactions among the components. It is a second fundamental goal of the program to understand and be able to express these interactions, to advance wetlands science and the management of urban wetlands and stormwater. Expression could come in the form of qualitative descriptions, relatively simple conceptual models, or more comprehensive mathematical algorithms. The extent to which definition of these interactions can be developed will determine the thoroughness with which management guidelines and new scientific knowledge can be generated by this research program.

Introduction

19

FIGURE 3 Typical monitoring plan (Patterson Creek 12 wetland).

The stormwater impact study examined the five major structural components of wetlands: (1) hydrology, (2) water quality, (3) soils, (4) plants, and (5) animals. Figure 3 presents a typical plan for monitoring of these components. A crest stage gauge was used to register the maximum water level since the preceding monitoring occasion, and a staff gauge gave the instantaneous water level. These readings provided the basis for hydrologic analysis, as detailed in Chapter 1, Morphology and Hydrology. Samples for water quality analysis were taken from the water column in an open water pool, and soil samples were collected at either three or four locations as described in Chapter 2, Water Quality and Soils. Plant cover by species was determined along one or more transect lines, depending on the wetland size and complexity of water and vegetation zones. Foliar tissue was sampled for analysis of metals content, and plant standing crop was cut for measurement of biomass gravimetrically. More on the methods used in these monitoring activities is included in Chapter 3. Adult insect emergence was continuously monitored using triplicate

20


emergence traps (see Chapter 4). Amphibian breeding success was monitored along transects (labeled Herp. A, B, and C in Figure 3). Adult amphibians as well as small mammals were live-trapped along other transects (labeled Mammal line A, B). Chapters 5 and 7 address amphibian and small mammal communities, respectively, in wetlands and elaborate on the methods used. Birds were censused at stations as described in Chapter 6.

DEFINITION OF WATERSHED AND SURROUNDING LANDSCAPE CHARACTERISTICS Essential to understanding the relationships between urban stormwater discharge and wetlands ecology was definition of the characteristics of wetland watersheds and surrounding landscapes. Each land use includes distinctive features, such as imperviousness and vegetative cover that directly affect wetland conditions.118 Use of geographical information in the analysis of the effects of urbanization on wetlands allows the linking of effects with specific land use changes associated with urban development. To this end, the program used a geographical information system (GIS) to inventory land uses in the watersheds of the study wetlands (see Table 1).118 The GIS furnished quantitative and graphical representations of land use patterns. Study sites were located on U.S. Geographical Survey 7.5-minute-series topographic maps and the maps were used to locate wetland and watershed boundaries. Aerial photographs from 1989 were digitized into a computer database and used to delineate wetland boundaries on the basis of wetland vegetation and open water. Land uses were classified according to a standard land use classification scheme. The GIS provided the areas of watersheds, wetlands, and land uses. These data were expressed in three ways: 1. Wetland and watershed areas in hectares; 2. Watershed land uses and vegetative cover as percentages of watershed areas; and 3. Ratios of the areas of watersheds, land uses, and vegetative cover to wetland areas. The most important quantities yielded by the third method were the ratios of watershed and wetland areas (wetland areas were subtracted from their watershed areas in calculating these ratios). The method also was used to determine the ratios of impervious and forested areas to wetland areas. GIS data obtained in 1989 were updated through visual examination of 1995 aerial photographs. In addition, in 1996, the same information was developed for 1000-m bands of the landscapes surrounding the study wetlands using 1995 satellite images. With regard to calculating watershed imperviousness, the program found that the relevant literature generally did not provide the level of detail necessary to establish the relationships between imperviousness and the land use definitions used in the GIS inventory. The program, therefore, relied on a variety of sources linking specific land uses to imperviousness levels. Estimates of imperviousness were made

Introduction

21

using values from the literature for similar land uses and adjusting them as necessary with best professional judgment.118-120 Effective Impervious Area (EIA) represents the impervious area that is actually connected to constructed drainage systems. This value was estimated as a proportion of Total Impervious Area (TIA) according to the formula EIA = 0.15 ∗ TIA1.41.119 This equation was developed in Denver and its accuracy (correlation coefficient = 0.98 and standard error = 0.075) probably varies in other areas. However, the author’s estimates were compatible with those in Puget Sound lowland hydrologic models.121 After determining EIA and TIA values for each land use, EIAs for entire watersheds were determined using the formula EIADB = Σ1 → k (EIAk ∗ LUk), where EIADB is the percentage of watershed area that is effectively impervious, k corresponds to the land uses inventoried in the basin, EIAk is the percentage of watershed area associated with land use k, and LUk is the percentage of the watershed classified as land use k. TIAs were calculated using the same formula.

ORGANIZATION OF THE MONOGRAPH The chapters that follow trace the major areas of progress in filling in the conceptual framework presented in Figure 2. Section II provides several chapters describing the ecology of the palustrine wetlands of the central Puget Sound lowlands, organized according to the major structural components monitored during the program. Section III presents five chapters assessing the effects of urban stormwater and other influences of urbanization observed during the study. Finally, Section IV makes recommendations for managing urban stormwater to protect wetlands in urbanizing watersheds.

REFERENCES 1. Athanas, C., Wetlands creation for stormwater treatment, in J. Zelanzny and J. S. Feierabend, Eds., Increasing Our Wetland Resources, National Wildlife Federation, Washington, D.C., 1988, p. 61. 2. McArthur, B. H., The use of isolated wetlands in Florida for stormwater treatment, in Wetlands: Concerns and Successes, Proc. Am. Water Resour. Assoc. Symp., D. N. Fisk, Ed., Tampa, FL, Sept. 17–22, 1989, p. 185. 3. Chan, E., T. A. Bursztynsky, N. Hantzsche, and Y. J. Litwin, The Use of Wetlands for Water Pollution Control, EPA-6-/S2-82-068, NTIS PB83-107466, U.S. Environmental Protection Agency, Municipal Environmental Research Laboratory, Cincinnati, Ohio, 1981. 4. Hickok, E. A., Wetlands for the control of urban stormwater, in Proceedings, National Conference on Urban Erosion and Sediment Control: Institutions and Technology, W. L. Downing, Ed., EPA 905/9-80-002, U.S. Environmental Protection Agency, Washington, D.C., 1980, p. 79. 5. Lakatos, D. F. and L. J. McNemar, Wetlands and stormwater pollution management, in Proceedings of a National Symposium: Wetland Hydrology, J. A. Kusler and G. Brooks, Eds., Association of State Wetland Managers, Berne, NY, 1988, p. 214. 6. Livingston, E. H., The use of wetlands for urban stormwater management, in Design of Urban Runoff Quality Controls, L. A. Roesner, B. Urbonas, and M. B. Sonnen, Eds., American Society of Civil Engineers, New York, NY, 1989, p. 467.

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Wetlands and Urbanization: Implications for the Future 7. U.S. Congress, Office of Technology Assessment, Wetlands: Their Use and Regulation, OTA-0-206. U.S. Government Printing Office, Washington, D.C., 1984. 8. Zedler, J. B. and M. E. Kentula, Wetlands Research Plan, EPA/600/3-86/009, NTIS PB86-158656, U.S. Environmental Protection Agency, Environmental Research Laboratory, Corvallis, OR, 1986. 9. Newton, R. B., The Effects of Stormwater Surface Runoff on Freshwater Wetlands: A Review of the Literature and Annotated Bibliography, Publication 90-2, University of Massachusetts, Environmental Institute, Amherst, MA, 1989. 10. Brown, R. G., Effects of Wetlands on Quality of Runoff Entering Lakes in the Twin Cities Metropolitan Area, Minnesota, Water Resources Investigations Report 85-4170, U.S. Geological Survey, Washington, D.C., 1985. 11. Canning, D. J., Urban Runoff Water Quality: Effects and Management Options, Shorelands Technical Advisory Paper No. 4, 2nd ed., Washington Department of Ecology, Shorelands and Coastal Zone Management Program, Olympia, WA, 1988. 12. ABAG (Association of Bay Area Governments), Urban Stormwater Treatment at Coyote Hills Marsh. Association of Bay Area Governments, Oakland, CA, 1986. 13. Woodward-Clyde Consultants, The Use of Wetlands for Controlling Stormwater Pollution (Draft). U.S. Environmental Protection Agency, Region 5, Water Division, Watershed Management Unit, Chicago, IL, 1991. 14. Silverman, G. S., Seasonal Fresh Water Wetlands Development and Potential for Urban Runoff Treatment in the San Francisco Bay Area, Ph.D. thesis, University of California, Los Angeles, 1983. 15. U.S. Environmental Protection Agency, Freshwater Wetlands for Wastewater Management: Environmental Assessment Handbook, EPA 904/9-85-135, U.S. Environmental Protection Agency, Region 4, Atlanta, GA, 1985. 16. Wentz, W. A., Ecological/environmental perspectives on the use of wetlands in water treatment, in Aquatic Plants for Water Treatment and Resource Recovery, K. R. Reddy and W. H. Smith, Eds., Magnolia Publishing, Orlando, FL, 1987, p. 17. 17. Benforado, J., Ecological considerations in wetland treatment of wastewater, in Selected Proceedings of the Midwest Conference on Wetland Values and Management, B. Richardson, Eds., Freshwater Society, Navarre, MN, 1981, p. 307. 18. Guntenspergen, G. and F. Stearns, Ecological limitations on wetland use for wastewater treatment, in Selected Proceedings of the Midwest Conference on Wetland Values and Management, B. Richardson, Ed., Freshwater Society, Navarre, MN, 1981, p. 272. 19. Sloey, W. E., F. L. Spangler, and C. W. Fetter, Jr., Management of freshwater wetlands for nutrient assimilation, in Freshwater Wetlands: Ecological Processes and Management Potential, R. E. Good et al., Eds., Academic Press, New York, 1978, p. 321. 20. Dawson, B., High hopes for cattails, Civ. Eng., 59, 5, 1989. 21. Heliotis, F. D., Wetland Systems for Wastewater Treatment: Operating Mechanisms and Implications for Design, IES Report 117, Institute for Environmental Studies, University of Wisconsin, Madison, 1982. 22. Brennan, K. M., Effects of wastewater on wetland animal communities, in Ecological Considerations in Wetlands Treatment of Wastewater, P. J. Godfrey et al., Eds., Van Nostrand Reinhold, New York, 1985, p. 199. 23. Kadlec, R. H., Northern natural wetland water treatment systems, in Aquatic Plants for Water Treatment and Resource Recovery, K. R. Reddy and W. H. Smith, Eds., Magnolia Publishing, Orlando, FL, 1987, p. 83.

Introduction

23

24. Stark, J. R. and R. G. Brown, Hydrology and water quality of a wetland used to receive wastewater effluent, St. Joseph, Minnesota, In Proceedings of a National Symposium: Wetland Hydrology, J. A. Kusler and G. Brooks, Eds., Association of State Wetland Managers, Berne, NY, 1988. 25. Bevis, F. B. and R. H. Kadlec, Effects of long-term discharge of wastewater on a northern Michigan wetland, in Abstr. Conf. Freshwater Wetlands and Sanitary Wastewater Disposal, Higgins Lake, MI, July 1979. 26. Whigham, D. F., R. L. Simpson, and K. Lee, The Effect of Sewage Effluent on the Structure and Function of a Freshwater Tidal Marsh Ecosystem, Rutgers University, Water Resources Research Institute, New Brunswick, NJ, 1980. 27. Boto, K. G. and W. H. Patrick, Jr., Role of wetlands in the removal of suspended sediments, in Wetland Functions and Values: The State of Our Understanding, P. E. Greeson et al., Eds., American Water Resources Association, Minneapolis, MN, 1978, p. 479. 28. Darnell, R. M., Impacts of Construction Activities in Wetlands of the United States, EPA-600/3-76-045, U.S. Environmental Protection Agency, Environmental Research Laboratory, Corvallis, OR, 1976. 29. Keddy, P. A., Freshwater wetlands human-induced changes: indirect effects must also be considered, Environ. Manage., 7(4), 299, 1983. 30. Weller, M. W., Issues and approaches in assessing cumulative impacts on waterbird habitats in wetlands, Environ. Manage., 12(5), 695, 1988. 31. U.S. Environmental Protection Agency, Natural Wetlands and Urban Stormwater: Potential Impacts and Management, 843-R-001, U.S. Environmental Protection Agency, Office of Water, Washington, D.C., 1993. 32. Johnson, P. G. and L. F. Dean, Stormwater Management Guidebook for Michigan Communities, Clinton River Watershed Council, Utica, MI, 1987. 33. Hemond, H. F. and J. Benoit, Cumulative impacts on water quality functions of wetlands, Environ. Manage., 12(5), 639, 1988. 34. Gosselink, J. G. and R. E. Turner, The role of hydrology in freshwater wetland ecosystems, in Freshwater Wetlands: Ecological Processes and Management Potential, R. E. Good et al., Eds., Academic Press, New York, 1978. 35. Mitsch, W. J. and J. G. Gosselink, Wetlands, 2nd ed., Van Nostrand Reinhold, New York, 1993. 36. Leopold, L. B., Hydrology for Urban Land Planning: A Guidebook on the Hydrologic Effects of Urban Land Use, U.S. Geological Survey Circular 554, U.S. Department of the Interior, Geological Survey, Washington, D.C., 1968. 37. Pedersen, E. R., The Use of Benthic Invertebrate Data for Evaluating Impacts of Urban Stormwater Runoff, M.S. thesis, University of Washington, College of Engineering, Seattle, 1981. 38. PSWQA (Puget Sound Water Quality Authority), Issue Paper: Nonpoint Source Pollution, PSWQA, Seattle, 1986. 39. Stockdale, E. C., Freshwater Wetlands, Urban Stormwater, and Nonpoint Pollution Control: A Literature Review and Annotated Bibliography, Washington Department of Ecology, Olympia, 1991. 40. Loucks, O. L., Restoration of the pulse control function of wetlands and its relationship to water quality objectives, in Wetlands Creation and Restoration: The Status of the Science: Vol. II, Perspectives, J. A. Kusler and M. E. Kentula, Eds., EPA/600/389/038, U.S. Environmental Protection Agency, Environmental Research Laboratory, Corvallis, OR, Pp. 55-65, 1989.

24

Wetlands and Urbanization: Implications for the Future 41. Adamus, P. R. and L. T. Stockwell, A Method for Wetland Functional Assessment: Volume 1, Critical Review and Evaluation, FHWA-1P-82-23, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., 1983. 42. Reinelt, L. E. and R. R. Horner, Characterization of the Hydrology and Water Quality of Palustrine Wetlands Affected by Urban Stormwater, PSWSMRP, Seattle, 1990. 43. Whigham, D. F., C. Chitterling, and B. Palmer, Impacts of freshwater wetlands on water quality: a landscape perspective, Environ. Manage., 12(5), 663, 1988. 44. Hopkinson, C. S. and J. W. Day, Jr., Modeling the relationship between development and stormwater and nutrient runoff, Environ. Manage., 4(4), 315, 1980 45. Azous, A., An Analysis of Urbanization Effects on Wetland Biological Communities, M. S. thesis. University of Washington, Department of Civil Engineering, Environmental Engineering and Science Program, Seattle, 1991. 46. Franklin, K. T. and R. E. Frenkel, Monitoring a Wetland Wastewater Treatment System at Cannon Beach, OR, U.S. Environmental Protection Agency, Region 10, Seattle, 1987. 47. Hickok, E. A., M. C. Hannaman, and N. C. Wenck, Urban Runoff Treatment Methods: Volume 1. Non-Structural Wetlands Treatment, EPA-600/2-77-217, Minnehaha Creek Watershed District, Wayzata, MN, 1977. 48. Lynard, W. G., E. J. Finnemore, J. A. Loop, and R. M. Finn, Urban Stormwater Management and Technology: Case Histories, EPA-600/8-80-035. U.S. Environmental Protection Agency, Washington, D.C., 1980. 49. Martin, E. H, Effectiveness of an urban runoff detention pond wetlands system, J. Environ. Eng., 114(4), 810, 1988. 50. Morris, F. A., M. K. Morris, T. S. Michaud, and L. R. Williams, Meadowland Natural Treatment Processes in the Lake Tahoe Basin: A Field Investigation (Final Report), EPA-600/54-81-026, NTIS PB81-185639, U.S. Environmental Protection Agency, Washington, D.C., 1981. 51. Oberts, G. L. and R. A. Osgood, The water quality effectiveness of a detention/wetland treatment system and its effect on an urban lake, presented at the 8th Annu. Int. Symp. Lake and Watershed Manage., St. Louis, MO, November 15–19, 1988. 52. Chan, E., Treatment of Stormwater Runoff by a Marsh/Flood Basin, Association of Bay Area Governments, Oakland, CA, 1979. 53. Ehrenfeld, J. G. and J. P. Schneider, The Sensitivity of Cedar Swamps to the Effects of Nonpoint Source Pollution Associated with Suburbanization on the New Jersey Pine Barrens, Rutgers University Press, New Brunswick, NJ, 1983. 54. Isabelle, P. S. et al., Effects of roadside snowmelt on wetland vegetation: an experimental study, J. Environ. Manage., 25(1), 57, 1987. 55. Morgan, M. D. and K. R. Philipp, The effect of agricultural and residential development on aquatic macrophytes in the New Jersey Pine Barrens, Biol. Conserv., 35, 143, 1986. 56. Mudrock, A. and J. A. Capobianco, Effects of treated effluent on a natural marsh, J. Water Pollut. Control Fed., 51(9), 2243, 1979. 57. Tilton, D. L. and R. H. Kadlec, The utilization of freshwater wetland for nutrient removal from secondarily treated wastewater effluent, J. Environ. Qual., 8, 328, 1979. 58. Galvin, D. V. and R. K. Moore, Toxicants in Urban Runoff, Toxicant Program, Report No. 2, Municipality of Metropolitan Seattle, Seattle, WA, 1982. 59. Harrill, R. L., Urbanization, water quality and stormwater management: a Maryland perspective, in Wetlands of the Chesapeake, Proc. Conf. held April 9–11, Easton, MD, 1985, p. 246.

Introduction

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60. Oberts, G. L., Water Quality Effects of Potential Urban Best Management Practices: A Literature Review, Techn. Bull. No. 97, Wisconsin Department of Natural Resources, Madison, 1977. 61. Hammer, D. A., Creating Freshwater Wetlands, Lewis Publishers, Chelsea, MI, 1992. 62. Fries, B. M., Fate of Phosphorus from Residential Stormwater Runoff in a Southern Hardwood Wetland, M.S. thesis. University of Central Florida, Orlando, 1986. 63. Lyon, J. G., R. D. Drobney, and C. E. Olson, Jr., Effects of Lake Michigan water levels on wetland soil chemistry and distribution of plants in the Straits of Mackinac, J. Great Lakes Res., 12(3), 175, 1986. 64. Brinson, M. M., Strategies for assessing the cumulative effects of wetland alteration on water quality, Environ. Manage., 12(5), 655, 1988. 65. ABAG (Association of Bay Area Governments), Treatment of Stormwater Runoff by a Marsh/Flood Basin (Interim Report), Association of Bay Area Governments, Oakland, CA, 1979. 66. Schiffer, D. M., Effects of Highway Runoff on the Quality of Water and Bed Sediments of Two Wetlands in Central Florida, Report No. 88-4200, U.S. Department of the Interior, Geological Survey, Washington, D.C., 1989. 67. Richardson, C. J., Wetlands as transformers, filters and sinks for nutrients, in Freshwater Wetlands: Perspectives on Natural, Managed and Degraded Ecosystems, 9th Symp., Charleston, SC, University of Georgia, Savannah River Ecology Laboratory, 1989. 68. Richardson, C. J., Mechanisms controlling phosphorus retention in freshwater wetlands, Science, 228, 1424, 1985. 69. Nichols, D. S., Capacity of natural wetlands to remove nutrients from wastewater, J. Water Pollut. Control Fed., 55(5), 495, 1983. 70. Marshland Wastewater Treatment Evaluation for the City of Black Diamond, R. W. Beck and Associates, Seattle, WA, 1985. 71. Horner, R. R., Long-term effects of urban stormwater on wetlands, in Design of Urban Runoff Controls, L. A. Roesner, B. Urbonas, and M. B. Sonnen, Eds., American Society of Civil Engineers, New York, 1989, p. 451. 72. Cooke, S. S., The effects of urban stormwater on wetland vegetation and soils: a long-term ecosystem monitoring study, in Puget Sound Res. ‘91: Proc., January 4–5, 1991, Seattle, WA, Puget Sound Water Quality Authority, Olympia, WA, 1991, p. 43. 73. Horner, R. R., F. B. Gutermuth, L. L. Conquest, and A. W. Johnson, Urban stormwater and Puget Trough wetlands, in Proc. First Annu. Meet. Puget Sound Res., Seattle, WA, March 18-19, 1988, Puget Sound Water Quality Authority, Seattle, 1988, p. 723. 74. Bedinger, M. W., Relation between forest species and flooding, in Wetland Functions and Values: The State of Our Understanding, P. E. Greeson et al., Eds., American Water Resources Association, Minneapolis, MN, 1979. 75. Green, W. E., Effect of water impoundment on tree mortality and growth, J. For., 45(2), 118, 1947. 76. Brink, V. C., Survival of plants under flood in the lower Fraser River Valley, British Columbia, Ecology, 35(1), 94, 1954. 77. Ahlgren, C. E. and H. L. Hansen, Some effects of temporary flooding on coniferous trees, J. For., 55, 647, 1957. 78. Rumberg, C. B. and W. A. Sawyer, Response of wet meadow vegetation to length and depth of surface water from wild flood irrigation, Agron. J., 57, 245, 1965. 79. Minore, D., Effects of Artificial Flooding on Seedling Survival and Growth of Six Northwestern Tree Species, Forest Service Reserve Note PNW-92, U.S. Department of Agriculture, Forest Service, Washington, D.C., 1968.

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Wetlands and Urbanization: Implications for the Future 80. Gill, C. J., The flooding tolerances of woody species: a review, For. Abst., 31, 671, 1970. 81. Cochran, P. H., Tolerances of lodgepole pine and ponderosa pine seedlings to high water tables, N. W. Sci., 46(4), 322, 1972. 82. Teskey, R. O. and T. M. Hinckley, Impact of Water Level Changes on Woody Riparian and Wetland Communities: Volume I — Plant and Soil Responses to Flooding, FWS/OBS-77/58, U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C., 1977. 83. Teskey, R. O. and T. M. Hinckley, Impact of Water Level Changes on Woody Riparian and Wetland Communities: Volume II — Southern Forest Region, FWS/OBS-77/59, U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C., 1977. 84. Teskey, R. O. and T. M. Hinckley, Impact of Water Level Changes on Woody Riparian and Wetland Communities: Volume III — The Central Forest Region, FWS/OBS-77/60, U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C., 1977. 85. Teskey, R. O. and T. M. Hinckley, Impact of Water Level Changes on Woody Riparian and Wetland Communities: Volume IV — Eastern Deciduous Forest Region, FWS/OBS-78/87, U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C., 1977. 86. Whitlow, T. H. and R. W. Harris, Flood Tolerance in Plants: A State of the Art Review, Techn. Rep. E-79-2, U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS, 1979. 87. Davis, G. B. and M. M. Brinson, Responses of Submerged Vascular Plant Communities to Environmental Change, FWS/OBS-79/33, U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C., 1980. 88. Walters, A. M., R. O. Teskey, and T. M. Hinckley, Impact of Water Level Changes on Woody Riparian and Wetland Communities: Volume VIII — Pacific Northwest and Rocky Mountain Regions, FWS/OBS-78/94, U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C., 1980. 89. McKnight, J. S., D. D. Hook, O. G. Langdon, and R. L. Johnson, Flood tolerance and related characteristics of trees of the bottomland forest of the southern United States, in Wetlands of Bottomland Hardwood Forests, J. R. Clark and J. Benforado, Eds., Elsevier, New York, 1981, p. 29. 90. Chapman, R. J., T. M. Hinckley, L. C. Lee, and R. O. Teskey, Impact of Water Level Changes on Woody Riparian and Wetland Communities: Volume X — Index and Addendum to Volumes I-VIII, U.S. Department of the Interior, Fish and Wildlife Service, Eastern Energy and Land Use Team, Kearneysville, WV, 1982. 91. Jackson, M. B. and M. C. Drew, Effects of flooding on growth and metabolism of herbaceous plants, in Flooding and Plant Growth, T. T. Kozlowski (ed.), Academic Press, San Diego, 1984. 92. Kozlowski, T. T., Ed., Flooding and Plant Growth, Academic Press, New York, 1984, p. 47. 93. Thibodeau, F. R. and N. H. Nickerson, Changes in a wetland plant association induced by impoundment and draining, Biol. Conserv., 33, 269, 1985. 94. Gunderson, L. H., J. R. Stenberg, and A. K. Herndon, Tolerance of five hardwood species to flooding regimes, in Interdisciplinary Approaches to Freshwater Wetlands Research, D. A. Wilcox, Ed., Michigan State University Press, East Lansing, 1988, p. 119. 95. Kadlec, J. A., Effects of a drawdown on a waterfowl impoundment, Ecology, 43, 267, 1962. 96. Niering, W. A., Effects of Stormwater Runoff on Wetland Vegetation, unpublished report (cited in U.S. EPA 1993), 1989.

Introduction

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97. van der Valk, A. G., Response of wetland vegetation to a change in water level, in Wetland Management and Restoration, C. M. Finlayson and T. Larson, Eds., Rep. 3992, Swedish Environmental Protection Agency, Stockholm, 1991. 98. Conner, W. H., J. G. Gosselink, and R. T. Parrondo, Comparison of the vegetation of three Louisiana swamp sites with different flooding regimes, Am. J. Bot., 68, 320, 1981. 99. Gomez, M. M. and F. P. Day, Litter nutrient content and production in the Great Dismal Swamp, Virginia, Am. J. Bot., 69, 1314, 1982. 100. Cooke, S. S. and A. L. Azous, Effects of Urban Stormwater Runoff and Urbanization on Palustrine Wetland Vegetation, A Report to the U. S. Environmental Protection Agency Region 10, Seattle, 1993. 101. Kadlec, J. A., Nutrient dynamics in wetlands, in Aquatic Plants for Water Treatment and Resource Recovery, K. R. Reddy and W. H. Smith, Eds., Magnolia Publishing, Orlando, 1987, p. 393. 102. Wickcliff, C., H. J. Evans, K. K. Carter, and S. A. Russell, Cadmium effects on the nitrogen fixation system of red alder, J. Environ. Qual., 9, 180, 1980. 103. Brown, B. T. and B. M. Rattigan, Toxicity of soluble copper and other metal ions in Eleodea Canadensis, Environ. Pollut., 21, 303, 1979. 104. Portele, G. J., The Effects of Highway Runoff on Aquatic Biota in the Metropolitan Seattle Area, M.S. thesis, University of Washington, Department of Civil Engineering, Seattle, 1981. 105. Nordby, C. S. and J. B. Zedler, Responses of fish and macrobenthic assemblages to hydrologic disturbances in Tijuana Estuary and Los Peñasquitos Lagoon, CA, Estuaries, 14(1), 80, 1991. 106. Marshall, W. A., The Effect of Stormdrain Runoff on Algal Growth in Nearshore Areas of Lake Sammamish, M.S. thesis, University of Washington, Department of Civil Engineering, Seattle, 1980. 107. Minton, S. A., Jr., The fate of amphibians and reptiles in a suburban area, J. Herpetol., 2(3–4), 113, 1968. 108. Lloyd-Evans, T. L., Use of Wetland for Stormwater Detention Effects on Wildlife Habitat, Manomet Bird Observatory (cited in Azous, 1991), 1989. 109. Richter, K. O., A. Azous, S. S. Cooke, R. Wisseman, and R. Horner, Effects of Stormwater Runoff on Wetland Zoology and Wetland Soils Characterization and Analysis, PSWSMRP, Seattle, WA, 1991. 110. Johnsgrad, P. A., Effects of water fluctuation and vegetation change on bird populations, particularly waterfowl, Ecology, 37, 689, 1956. 111. Richter, K. O. and R. Wisseman, Effects of Stormwater Runoff on Wetland Zoology, PSWSMRP, Seattle, WA, 1990. 112. Bursztynsky, T. A., Personal communication to E. C. Stockdale, King County, Resources Planning Section (cited in Stockdale, 1991), 1986. 113. Weller, M. W., The influence of hydrologic maxima and minima on wildlife habitat and production values of wetlands, in Wetland Hydrology, J. A. Kusler and G. Brooks, Eds., Association of State Wetland Managers, Chicago, 1987. 114. Stockdale, E. C., The Use of Wetlands for Stormwater Management and Nonpoint Pollution Control: A Review of the Literature, Washington Department of Ecology, Olympia, 1986. 115. Stockdale, E. C., Viability of Freshwater Wetlands for Urban Surface Water Management and Nonpoint Pollution Control: An Annotated Bibliography, Washington Department of Ecology, Olympia, 1986. 116. Reinelt, L. E. and R. R. Horner, Pollutant removal from stormwater runoff by palustrine wetlands based on a comprehensive budget, Ecol. Eng., 4, 77, 1995.

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117. Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe, Classification of Wetlands and Deepwater Habitats of the United States, FWS/OBS-79/31, U.S. Fish and Wildlife Service, Washington, D.C., 1979. 118. Taylor, B. L., The Influence of Wetland and Watershed Morphological Characteristics on Wetland Hydrology and Relationships to Wetland Vegetation Communities, M.S. thesis, University of Washington, Department of Civil Engineering, Seattle, 1993. 119. Alley, W. M. and J. E. Veenhuis, Effective impervious area in urban runoff modeling, J. Hydraul. Eng., 109(2), 313, 1983. 120. Prych, E. A. and J. C. Ebbert, Quantity and Quality of Storm Runoff from Three Urban Catchments in Bellevue, Washington, Water Resources Investigations Report 86-4000, U. S. Geological Survey, Tacoma, 1986. 121. PEI/Barrett Consulting Group, Snoqualmie Ridge Draft Master Drainage Plan, Bellevue, WA, 1990. 122. U.S. Environmental Protection Agency, Results of the Nationwide Urban Runoff Program: Executive Summary, NTIS PB84-185545, U.S. Environmental Protection Agency, Water Planning Division, Washington, D.C., 1983.

Section II Descriptive Ecology of Freshwater Wetlands in the Central Puget Sound Basin

1

Morphology and Hydrology Lorin E. Reinelt, Brian L. Taylor, and Richard R. Horner

CONTENTS Introduction..............................................................................................................31 Puget Sound Wetlands and Stormwater Management Research Program .............32 Wetlands in Urbanizing Areas.................................................................................33 Wetland Hydrologic Functions................................................................................33 Hydrology of Palustrine Wetlands ..........................................................................33 Precipitation ....................................................................................................34 Surface Inflows ...............................................................................................34 Groundwater ...................................................................................................34 Change in Wetland Storage ............................................................................35 Evapotranspiration ..........................................................................................35 Surface Outflow ..............................................................................................35 Research Methods and Wetland Descriptors...........................................................36 Wetland Morphology ......................................................................................36 Watershed Characteristics...............................................................................36 Watershed Imperviousness .............................................................................37 Watershed Soils ..............................................................................................38 Wetland Hydrology..................................................................................................39 Wetland Water Level Measurements and Fluctuation ...................................39 Seasonal Fluctuation in Wetland Water Levels..............................................39 Length of Summer Dry Period.......................................................................40 Results and the Conceptual Model .........................................................................40 Water Level Fluctuation Patterns ...................................................................40 Conceptual Model of Influences on Wetland Hydroperiod ...........................41 Conclusions..............................................................................................................41 Acknowledgments....................................................................................................43 References................................................................................................................44

INTRODUCTION This chapter provides an overview of the morphologic and hydrologic characteristics of palustrine (depressional freshwater) wetlands and their watersheds in the central 1-56670-386-7/01/$0.00+$.50 © 2001 by CRC Press LLC

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Puget Sound Basin. Natural and anthropogenic factors that affect wetland morphology and hydrology are discussed, with particular attention to the effects of development (typically the conversion of forested lands to urban areas) on changing watershed and wetland hydrology. It was concluded that wetland water level fluctuation (WLF) estimates, measured with staff and crest-stage gauges, provide a good overall indicator of wetland hydrologic conditions. Analysis methods and materials used in the research program are also presented. Wetlands are ecosystems that develop at the interface of aquatic and terrestrial environments when hydrologic conditions are suitable. Wetlands are recognized as biologically productive ecosystems offering extensive, high-quality habitat for a diverse array of terrestrial and aquatic species, as well as multiple beneficial uses for humans, including flood control, groundwater recharge, and water quality treatment. However, as urbanization of natural landscapes occurs, some or all of the functions and values of wetlands may be affected. Some wetlands may be impacted by direct activities such as filling, draining, or outlet modification, while others may be affected by secondary impacts, including increased or decreased quantity and reduced quality of inflow water. The morphology of a wetland and the wetland’s position within the landscape greatly influences habitat characteristics. Morphology is used here to describe the wetland’s physical shape and form. As a result of a wetland’s shape, it may contain significant pooled areas with little or no flow gradient (termed an open-water system), or alternatively, it may show evidence of channelization and contain a significant flow gradient (termed a flow-through system). In some instances, a wetland may also form in a local or closed depression (termed a depressional system). The outlet condition of a wetland, as defined by the degree of flow constriction, has a direct effect on wetland hydrology and hydroperiod. Finally, a wetland’s position in the landscape is also a key factor affecting wetland hydrologic conditions. Palustrine (isolated, freshwater) wetlands usually have relatively small contributing watersheds and often occur in areas with groundwater discharge conditions. Hydrology is probably the single most important determinant for the establishment and maintenance of specific types of wetlands and wetland processes.1 Water depth, flow patterns, and the duration and frequency of inundation influence the biochemistry of the soils and are major factors in the selection of wetland biota. Thus, changes in wetland hydrology may influence significantly the soils, plants, and animals of particular wetland systems. Precipitation, surface water inflow and outflow, groundwater exchange and evapotranspiration, along with the physical features noted above, are the major factors that influence the hydrology of palustrine wetlands.

PUGET SOUND WETLANDS AND STORMWATER MANAGEMENT RESEARCH PROGRAM The Puget Sound Wetlands and Stormwater Management Research Program was established to determine the effects of urban stormwater on wetlands and the effect of wetlands on the quality of urban stormwater. There are two primary components of the research program: (1) a study of the long-term effects of urban stormwater on wetlands, and (2) a study of the water quality benefits to downstream receiving

Morphology and Hydrology

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waters as urban stormwater flows through wetlands. In both studies, the hydrologic and morphologic conditions of the wetlands had a direct effect on observations involving water quality, soils, and the plant and animal communities. We present here hydrologic information gained from a broad overview of the hydrology of 19 wetlands representing a variety of watershed development conditions studied from 1988 to 1995. The discussion also covers information on the hydrology of two wetlands, one each in an urban (B3I) and undeveloped (PC12) watershed, intensively studied from 1988 to 1990. Study site locations are shown in Section I, Figure 1-1.

WETLANDS IN URBANIZING AREAS Wetlands have received increased attention in recent years as a result of continuing wetland losses and impacts resulting from new development. In urbanizing areas, the quantity and quality of stormwater can change significantly as a result of landuse conversion in a watershed. Increases in the quantity of stormwater usually result from new impervious surfaces (e.g., roads, buildings), installation of storm sewer piping systems, and removal of trees and other vegetation in the watershed. On the other hand, decreased inflow of water to wetlands can result from modifications in surface and groundwater flows. Wetland hydrology is often described in terms of its hydroperiod, the pattern of fluctuating water levels resulting from the balance between water inflows and outflows, topography, subsurface soil, geology, and groundwater conditions.1 Seasonal water level changes have been described as the heartbeat of Pacific Northwest palustrine systems.2 For cases where wetlands are the primary receiving water for urban stormwater from new developments, the effects of watershed changes will be manifested through changes in the hydrology of wetlands.

WETLAND HYDROLOGIC FUNCTIONS Wetlands provide many important hydrologic, ecological, and water quality functions. Specific hydrologic functions include flood protection, groundwater recharge, and streamflow maintenance. Wetlands provide flood protection by holding excess runoff after storms, before slowly releasing it to surface waters. While wetlands may not prevent flooding, they can lower flood peaks by providing detention of storm flows. Wetlands that are connected to groundwater or aquifers provide important recharge waters. Wetlands retain water, allowing time for surface waters to infiltrate into soils and replenish groundwater. During periods of low streamflow, the slow discharge of groundwater maintains instream flows. The connection of wetlands with streamflows and groundwater make them essential in the proper functioning of the hydrologic cycle.

HYDROLOGY OF PALUSTRINE WETLANDS The hydrology of palustrine wetlands is governed by the following components: precipitation, evapotranspiration, surface inflow, surface outflow, groundwater

34


EVAPOTRANSPIRATION PRECIPITATION

SURFACE SURFACE

INFLOWS CHANGE IN STORAGE

OUTFLOWS

GROUNDWATER

GROUNDWATER

OUTFLOWS

INFLOWS

FIGURE 1-1 Wetland water budget components.

exchange, and change in wetland storage (see Figure 1-1). In a hydrologic balance, these components are represented by the following equation: P + I ± G ± S = ET + O

(1-1)

where P = precipitation, I = surface inflow, G = groundwater exchange, S = change in wetland storage, ET = evapotranspiration, and O = surface outflow.3

PRECIPITATION Precipitation is determined by regional climate and topography. Approximately 75% of the total annual rainfall occurs from October to March during a well-defined wet season in the Puget Sound region. Generally, annual precipitation totals across central Puget Sound increase further east with increasing elevation. Rainfall tends to be more uniform geographically during the wet season, and more variable and intense during short dry-season cloudbursts.

SURFACE INFLOWS Surface inflows result from runoff generation in the wetland’s watershed. The quantity of surface inflows are determined by watershed land characteristics such as cover (e.g., impervious surface, forest), soils, slopes, as well as the wetland-to-watershed ratios. The rate of water delivery to the wetland is also affected by the predominant flow type in the watershed (e.g., overland or sheet flow, subsurface flow or interflow, concentrated flow). Generally, as a watershed becomes more developed, with more constructed storm drainage systems, the more rapid the hydrologic response in the watershed.

GROUNDWATER The role and influence of groundwater on wetland hydrology is highly variable. The exchange of water between the wetland and groundwater is governed by the relative elevations of surface water in the wetland and surrounding groundwater, as well as


35

soil permeability, local geology and topography. Numerous studies have discussed the importance of groundwater in maintaining wetland hydrology.1,4,5 Wetlands can be discharge or recharge zones for groundwater, or both, depending on the time of year. The palustrine wetlands studied in this research are predominantly groundwater discharge zones (water discharges from groundwater to the wetland). Groundwater flow to wetlands can be quantitatively estimated using Darcy’s law, an empirical law governing groundwater flow: Q = –KA dH/dL

(1-2)

where K = hydraulic conductivity, dH/dL = the hydraulic or piezometric gradient and A = cross-sectional area or control surface across which groundwater flows. In the detailed study of two wetlands, shallow and deep piezometers were installed at both wetlands to estimate the horizontal and vertical components, respectively, of groundwater flow to the wetlands.

CHANGE

IN

WETLAND STORAGE

Wetland storage changes seasonally and in response to storm events. The water storage can be estimated as the mean water depth of the wetland multiplied by the area of the wetland.1 Seasonal changes in wetland storage are attributable to the local patterns of precipitation and evapotranspiration. It has been asserted that the prime factor controlling seasonal fluctuation is drainage basin topography and that wetland water levels generally coincide with regional groundwater levels.6 Also observed is that steep slopes adjacent to a wetland can lead to increased groundwater inputs, particularly on a seasonal basis.5 Event changes in wetland storage result from increased surface or groundwater inputs associated with precipitation. This observation of hydrologic change is referred to as water level fluctuation (WLF). It is estimated for an occasion as the difference between the instantaneous staff-gauge measurement and a crest-stage measurement of the peak water level (since the previous sampling occasion).7-9

EVAPOTRANSPIRATION Evapotranspiration (ET) consists of water that evaporates from wetland water or soils combined with the water that passes through vascular plants that is transpired to the atmosphere. Solar radiation, temperature, wind speed, and vapor pressure are the main factors influencing evaporation rates.10 The ratio of ET to evaporation varies widely depending on vegetation type and site conditions. Reported ET ratios vary between 0.67 and 1.9.11-13 Generally, emergent wetland vegetation transpires more than woody vegetation; however, factors such as plant density also affect transpiration rates. Evapotranspiration is greatest from May to August, exceeding 100 mm per month, and least from November to March.

SURFACE OUTFLOW Surface outflows are affected by all the hydrologic factors noted above. For wetlands with relatively large watersheds, outflows are often comparable in magnitude to

36


inflows. The physical features that affect surface outflows include outlet conditions, wetland-to-watershed ratios, and wetland morphometry.

RESEARCH METHODS AND WETLAND DESCRIPTORS Many of the methods and materials used for morphologic, hydrologic, and watershed data collection were previously reported in PSWSMRP papers.7,9,14 Here, we provide a summary of the methods, with additional information on data processing and analysis.

WETLAND MORPHOLOGY Three different measures of wetland morphology that influence the hydrology and hydroperiod of wetlands were defined and include wetland type (open water, flow through, depressional), outlet condition, and wetland-to-watershed ratio.7 Wetlands were classified as open-water systems if significant open water pools were present and surface water velocities were predominantly low (less than 5.0 cm/s). Wetlands were classified as flow-through systems if there was evidence of channelization and significant water velocities. All depressional wetlands were also open water wetlands. Outlet conditions were defined by level of constriction as high (e.g., undersized culvert, closed depression, confined beaver dam), or low to moderate (e.g., overland flow to stream, oversized culvert, broad bulkhead or beaver dam).9,14 Wetland-towatershed ratios was determined by the area of wetland in relationship to the contributing watershed. Watershed areas were delineated based on U.S. Geological Survey (USGS) quadrangle map contours and wetland areas were obtained from the King County Wetlands Inventory.15 The hydroperiod of wetlands with low wetlandto-watershed ratios (less than 0.05) tends to be dominated by surface inflows, whereas wetlands with higher ratios are more influenced by regional groundwater conditions.

WATERSHED CHARACTERISTICS Changes in land use ultimately affect wetlands receiving water from an urbanizing drainage basin. Different land uses have unique combinations of factors that directly affect watershed hydrology, such as imperviousness and vegetative cover. By collecting information about drainage basin land use, it is possible to link wetland hydroperiod characteristics to specific land uses, as well as general changes associated with urban development. A geographic information system (GIS) was developed to manage land use data for the watersheds of the study wetlands, and to facilitate quantitative and graphical analysis of land-use patterns. Land-use classifications, based on a national standard, were determined from 1989 aerial photographs and subsequently digitized for viewing and analysis using computer software.14,16 For each study site, the GIS contained information about the total watershed, wetland area, and the area of watershed in each land use type (e.g., urban, agriculture, forest).


37

TABLE 1-1 Total Impervious (TIA) and Effective Impervious Areas (EIA) Associated with Land Uses Code

National Standard

TIA%

EIA%

Reference Number or Source

111 112 113 114 115 120 121 123 124 131 132 144 151 152 155 160 161 162 171 172 190 192 193 200 300 400–430 440

Low Density SFR (7 units/acre) Commercial (general) Retail sales and services Offices and professional services Hotels and Motels Light Industrial Heavy Industrial Freeway Right-of-way Energy Facilities Water Supply Facilities Utility Right-of-way Community Facilities (general) Educational Facilities Religious Facilities Golf Courses Parks Open Land (general) Land being developed Open space — designated Agricultural Land Grassland Forest Lands Clearcut areas

66% 5.1 173 2.9 >53% 6.3 67

72.5 230.0 63.8 88% 46.0 190 142.4 275.0 72.8 51% 160.0 161 150.9 271.0 85.5 57% 132.2 61

8.5 >185% 2.0 204 21.6 >235% 2.8 175 15.1 >164% 4.0 66

129.3 >216% 21.0 205 266.8 >212% 43.0 177 104.4 >153% 32.0 67

484.6 >132% 111.5 206 847.2 >142% 304.0 177 239.4 >61% 376.0 67

47.6 >271% 6.0 200 37.9 >120% 16.0 172 31.2 79.0 15.7 50% 28.2 65

52.3 850.0 86.6 166% 29.0 206 92.5 780.0 91.8 99% 70.0 177 109.5 1940.0 233.5 213% 69.0 67

>271.3 6240.0 >1000.4 >369% 9.0 206 >2664.8 359550.0 >27341.7 >1026% 46.0 173 >968.6 38000.0 >4752.8 >491% 61.0 66

2.7 >80% 51% 62% 105% 1.0 136 2.7 >79% 3.0 122 4.0 >89% 5.0 44

8.3 >99% 5.0 136.0 7.2 >73% 8.0 122.0 16.7 >83% 20.0 44.0

Note: Nonurban watersheds (N) = less than 4% impervious land cover and greater than or equal to 40% forest. Highly urbanized watersheds (H) = greater than or equal to 20% impervious and less than or equal to 7% forest. Moderately urbanized watersheds (M) = wetlands not fitting either of the other categories.


M

Statistic

Water Quality and Soils

51

to 7% forest. Those wetlands not fitting either of the other categories were classified as moderately urbanized watersheds (M).11 This classification scheme was developed for analysis of the probable origin of soil metals, and was used for water quality as well. Characteristics of the individual watersheds can be found in Section I, Table 1. Indeterminate statistics (greater than or less than a given value) are the result of some measurements being below detection or, in the case of FC, bacterial colonies too numerous to count in some very concentrated samples. Examination of Table 2-1 reveals several general points about wetland water quality. First, excepting pH, concentrations varied greatly, as indicated by the relatively high coefficients of variation (CV). The principal sources of water quality variability are examined later in the chapter. Fecal coliform was the most variable of the analyses overall, followed by TSS and NH3-N. Other than for pH, DO, and conductivity, medians were usually lower than arithmetic means, signifying the influence on means, but not on medians, exerted by a relatively few high values. This trend is consistent with a lognormal probability distribution of values, a distribution frequently observed in environmental data.12 In the nonurban wetlands, a cursory comparison of the Table 2-1 medians, shows that pH rose slightly and DO marginally declined with increasing urbanization. Conductivity and NH3-N increased substantially from nonurban to moderately urban wetlands but actually were a bit lower in highly urbanized cases. NO3+NO2-N and TP increased from N to M status, but not further, with H status. Cu showed little difference among categories, but many values were below detection. The remaining variables (TSS, SRP, FC, Pb, and Zn) all increased with each step up in urbanization level. A water quality portrait of Puget Sound Basin lowland palustrine wetlands relatively unaffected by humans, then, shows slightly acidic (median pH = 6.4) systems with DO often well below saturation, and in fact sometimes quite low (less than 4 mg/l). Dissolved substances are relatively low (most conductivity readings less than 50 µS/cm) but somewhat variable. Suspended solids are routinely low but quite variable, reflecting the strong influence of storm runoff events on TSS. Median total dissolved nitrogen concentrations (the sum of ammonia, nitrate, and nitrite) are more than 20 times as high as dissolved phosphorus, suggesting general plant and algal growth is generally limited by P. Some of the fairly abundant TP would become available over time to support photosynthesis, but probably not enough to modify the general picture. The low median fecal coliform indicates that most readings are very low (less than 10 CFU/100 ml), but a small number is so high that the mean is 30 times the median. Both mean and median heavy metals concentrations are in the low parts per billion range, with standard deviations just about identical to the means.

WETLAND WATER QUALITY

IN

CONTEXT

To proceed with a descriptive picture of regional wetland water quality, it is useful to provide some context for the quantitative information. This portion of the chapter discusses the statistical data with respect to informal criteria for separating the data into groups that can be associated with various factors that may influence the magnitudes. The account also gives a sense of how water quality compares in regional wetlands versus streams.

52


The informal criteria are based on several considerations and were slightly modified from past studies for this monograph.3 Some are regulatory standards applied to other water body types (water quality standards have not yet been adopted for wetlands in Washington). Others have generally recognized biological relevance, but some are simply arbitrary breakpoints in the data distributions. In all cases professional judgment was applied in adopting a numerical informal criterion. Table 2-2 gives the distribution of wetlands, using median values, among the three urbanization categories relative to the informal criteria. It also repeats the medians and means for each category from Table 2-1.

TABLE 2-2 Comparison of Medians of Water Quality Variables for Wetlands Not Experiencing Significant Urbanization Change (1988–1995) with Informal Criteria Nonurbanized (N) Variable pH

DO (mg/l)

Cond. (µS/cm)

TSS (mg/l)

NH3-N (µg/l)

NO3 + NO2-N (µg/l) TP (µg/l)

FC (CFU/100 ml)

Zn (µg/l) a

Moderately Urbanized (M)

Criterion median

mean

%a

median

5–6 6–7 7–8 6 200 5 100 500 50 100 10b

6.4 16.7 67.7 16.7 5.7 33.3 33.3 33.3 72 83.3 16.7 0 167% <MDL 77

56.9 >268% 5.1 132 18.2 >173% 6.1 68 40.1 >180% 10.0 75

63.2 850.0 103.2 163% 31.0 136 31.1 188.0 27.4 88% 24.2 70 68.7 310.0 68.8 100% 44.0 77

2.8 >84% 5.0 62 2.4 >74% <MDL 31 2.0 >62% 2.6 33

2.4 >93% 1.0 90 0.0 >0% <MDL 46 2.2 >82% <MDL 54

8.6 >95% 6.0 90 7.7 >107% 2.5 46 6.6 >75% 7.9 54

>254.4 6240.0 >1080.9 >425% 4.0 136 828.1 >272% 47.0 70 >273.4 >6000.0 >974.3 >356% 10.0 74


TABLE 2-3 Water Quality Statistics for Wetlands Not Experiencing Significant Urbanization Change (1988–1995) Grouped by Urbanization and Morphological Status

55

56

TABLE 2-3 (continued) Water Quality Statistics for Wetlands Not Experiencing Significant Urbanization Change (1988–1995) Grouped by Urbanization and Morphological Status

M/FT Flow Through

H/FT Flow Through

a

Statistic

pH

DO Cond. TSS NH3-N (mg/l) (µS/cm) (mg/l) (µg/l)

Mean Maximum St. Dev. CV Median n Mean Maximum St. Dev. CV Median n

6.99 7.88 0.53 8% 7.15 76 6.73 7.51 0.57 9% 6.88 52

3.7 >53% 7.6 98 2.9 >53% 6.3 67

182.7 275.0 54.5 30% 199.5 92 150.9 271.0 85.5 57% 132.2 61

25.9 >218% 4.4 99 15.1 >164% 4.0 66

See Table 2-1 for definitions of Urban Status abbreviations.

197.7 >161% 47.5 100 104.4 >153% 32.0 67

NO3+NO2-N (µg/l) 987.1 >110% 662.5 100 239.4 >61% 376.0 67

SRP (µg/l)

TP FC (µg/l) (CFU/100 ml)

Tot Cu (µg/l)

Tot Pb (µg/l)

Tot Zn (µg/l)

38.6 169.0 34.6 90% 29.0 97 31.2 79.0 15.7 50% 28.2 65

110.8 780.0 102.9 93% 85.0 100 109.5 1940.0 233.5 213% 69.0 67

1.7 >43% 5.0 45 2.5 >62% 5.0 29

2.9 >72% 5.0 68 4.0 >89% 5.0 44

7.6 >71% 8.0 68 16.7 >83% 20.0 44

>4452.2 359550.0 >36108.2 >811% 215.0 99 >968.6 38000.0 >4752.8 >491% 61.0 66


Urban Statusa & Morph.


57

in the rest of the year possibly as a result of greater fertilizer applications and lower water levels that concentrate nutrients. NO3+NO2-N values fluctuated greatly in the program wetlands, and tended to vary directly with DO.3 This association is another sign that nitrification moderated by the degree of aerobiosis has a strong influence on how much NO3+NO2-N will be found in a wetland water column. Medians and geometric means of fecal coliform (FC) and enterococcus bacteria were highly variable. Peak counts occurred most frequently in late August and September, and least often from mid-November through February.3 The monitoring program found that while most water quality parameters varied seasonally, NH3-N, SRP, TP, FC, and enterococcus were especially changeable.3

VARIATION

WITH

WETLAND MORPHOLOGY

Wetland morphology refers to its form and physical structure and includes its shape; perimeter length; internal horizontal dimensions; topography (also termed bathymetry), which is the pattern of elevation gradients; water inlet and outlet configurations; and water pooling and flow patterns. These factors establish zonation at early successional stages by determining the extent of inundation from place to place and the hydrodynamic characteristics of flow. From these structural zones stem vegetation composition, distribution, and productivity, and ultimately, the character of the animal communities. Of course, these biota in turn influence morphological development over time through detrital and sediment accretion and animal activities like burrowing and dam building by beavers. The various morphological characteristics entirely determine the flood-flow storage and alteration function of wetlands. Along with the friction produced by vegetation, they set the residence time of water within the wetland, which is a key regulator of sediment trapping, nutrient processing, and other water quality functions. Early work in the program determined that one aspect of morphology in particular, water pooling and flow patterns, had a substantial influence on wetland water quality.3,6 The wetlands in the study were classified as either open water (OW) or flow-through (FT) types. The OW systems contain significant pooled areas and possess little or no flow gradient, while the FT wetlands are often channelized and have a clear flow gradient. Using the first three years of data, it was found, unsurprisingly, that temperatures ranged higher in wetlands characterized by relatively large open pools, especially from May to September.3 On an annual basis, the photosynthetic pigments chlorophyll a and phaeophytin a attained higher concentrations in wetlands characterized by large open pools, which have greater light exposure and longer residence times, and ranged much higher than in flow-through wetlands during the growing season. Dissolved oxygen tended to be significantly lower than in flow-through wetlands during these periods. Table 2-4 summarizes statistics for the wetlands whose watersheds stayed relatively stable during the program broken down by urbanization and morphological status. Comparing open water vs. flow-through wetlands in the N and M categories, it can be seen that medians were higher, often substantially so, for flow-through than for open water wetlands in both urbanization categories for pH, DO, Cond,

58


TABLE 2-4 Distribution of Water Quality Data for Baseflow Samples from 50 Stream Sites15

Conductivity (µmho/cm) Suspended Solids (mg/l) Ammonia (µg/l) Nitrate+nitrite (µg/l) Temperature (C) Dissolved Oxygen (mg/l) Turbidity (NTU) Fecal coliform (org/100 ml) Enterococcus (org/100 ml) pH Total phosphorus (µg/l)

Maximum

75th Percentile

50th Percentile

25th Percentile

Minimum

30,900 12.6 190 3000 13.5 11.4 16.5 900 410 8.2 150

203 4.8 24 1100 11.1 11 2.7 220 170 7.6 66

130 3.4 15 630 10.6 10.4 1.8 100 53 7.5 48

104 2.8 13 320 10 9.6 1.4 49 22 7.3 32

53 1.6 5 73 8 5.8 0.7 7 5 6.9 13

NO3+NO2-N, SRP, FC, and Pb. In addition, the flow-through means were higher in moderately urbanized wetlands for TSS, NH3-N, TP, Cu, and Zn. Over all levels of urbanization flow-through wetland medians were higher for all water quality variables reported in the table. It is clear from these results that flow-through wetlands strongly tend to be less acidic and better oxygenated than open water sites, as would be expected. Humic acid-producing vegetation thrives in an environment with low inflow, and attendant nutrient income. In these ponded systems oxygen renewal from the atmosphere is not as efficient as in flowing water, and they are warmer and hence have lower oxygen solubility. Also, more primary production and more oxygen-consuming organic decomposition occurs in the relatively long period of water residence. It is also clear that flow-through wetlands generally have higher pollutant concentrations, probably due to the greater loading of pollutants by the flow, and reduced pollutant removal from the water column with the shorter hydraulic residence times. Concentrations of NO3+NO2-N exhibited one of the greatest disparities between open water and flow-through wetlands. In addition to greater loading introduced by the flow, this phenomenon is probably partially due to higher oxygen levels in flowthrough cases, which promote nitrification that converts ammonia to nitrite and then nitrate forms. In fact, ammonia differed between the two types of morphology much less than did NO3+NO2-N, suggesting that ammonia discharged to wetlands may be more effectively nitrified in flowing systems. Of course, these systems also support less decomposition by microorganisms and, thus, likely produce less ammonia internally than do open water wetlands. It must be noted that a preponderance of flow-through wetlands are in more urbanized areas, which certainly affects pollutant loading and may affect the strength of conclusions, although probably not the overall trends. It is possible that this skewed distribution is not just a coincidence but reflects the urban situation, in which


59

higher peak runoff flows, wetland filling, and stream channelization favor flowthrough over open water wetland conditions.

SOILS COLLECTION

AND

METHODS

Soil samples were collected once from each wetland during the months July–September in 1988 to 1990, 1993, and 1995. Soil sampling areas were selected 3 m to the side of vegetation transect lines at every point where the soil type appeared either to be transitional or completely different. Small soil cores or signs of vegetation change were the basis for judgment. Two to five samples, most commonly four, were collected from each wetland. The number had a relationship to the size and zonal complexity of the wetlands. This coverage was considered to be adequate because a synoptic study of 73 urban and rural wetlands early in the program found that there were no significant differences among wetland zones (e.g., open pool, inlet, scrub-shrub, and emergent) with respect to soil texture, organic content, pH, phosphorus, and nitrogen.15 Because oxidation-reduction potential and one metal were significantly different near inlets as compared to other locations, the inlet zone was emphasized in choosing sampling areas. Soil samples were collected with a corer consisting of a 10-cm (4-in.) diameter ABS plastic pipe section ground to a sharp tip. The corer was twisted into the soil with a wooden rod inserted horizontally through two holes near the top. Coring depth was 15 cm (6 in.). Samples were inserted immediately into plastic bags, air was extruded, and the bags were sealed with tape. They were then transported to one of several laboratories used in the different years. A standard 60-cm (2-ft) deep soil pit was dug at each sampling point not inundated above the surface. The pit was observed and notes were recorded for depth to water table (if within 60 cm of the surface), horizon definition (thickness of each layer and boundary type between), color (using Munsell notations), structure (grade, size, form, consistency, and moisture), and presence of roots and pores. Soil core samples were analyzed for the following constituents: General Characteristics

• Particle size distribution (PSD) • Percent organics as loss on ignition (LOI) • pH • Oxidation-reduction potential (redox)

Nutrients

Metals

• Total phosphorus (TP)

• Arsenic (As)

• Total Kjeldahl nitrogen (TKN)

• Cadmium (Cd) • Copper (Cu) • Lead (Pb)

Details on the general analytical methods, as well as the sampling program design, are reported elsewhere.4 A method for PSD, also termed soil texture, was developed during this program for soils with more than 5% organics, as most wetland

60


soils have. Texture is the measurement of the proportions of the various sizes of mineral particles in a soil, classified from largest to smallest as sand, silt, and clay (gravel, when significant, is also recognized in the texture classification). The analysis of any soil with more than 5% organic content must include a step that removes the organic material. Failure to remove the organic component may cause clumping of particles and render the results inaccurate. The revised PSD method is considered to be accurate for soils with up to 25% organics. At higher levels it is not accurate because of sample loss during organic removal preparation, especially in the clay component. Additional sources of detail on methods and findings are reported from the initial years.17-21 Soils methods and results have also been reported elsewhere.5,7,19

RESEARCH FINDINGS: A PORTRAIT OF PUGET SOUND BASIN WETLAND SOILS General Soil Characteristics and Nutrients Like water quality, soil quality exhibited extensive variability. Table 2-5 statistically summarizes the soils data, excluding PSD, for wetlands that did not experience significant urbanization change during the program. This set of wetlands had watersheds that ranged from low to moderate to highly urbanized. Coefficients of variation for the majority of the soil variables were generally in the approximate range of 75 to 150%, although some were much higher. CVs for pH were considerably lower than for other analytes for both soils and water, usually about 10 ± 3%. Similar to water quality variables, the soil variables in Table 2-5 usually exhibited medians lower than the means, except for redox and sometimes pH. Therefore, most of these data also are far from normally distributed, and are probably lognormal. Most wetlands had at least some pockets of peat of mainly sedge and grass origins, and their soils accordingly tended to be acidic.19 Among the different groupings of data in Table 2-5, median pH values were less than or equal to 6.1, except for highly urbanized cases, which were also flow-through systems. Overall, wetlands in highly urbanized watersheds had the highest median pH, followed by wetlands in moderately urbanized and then nonurbanized watersheds. Flow-through wetlands overall and in the N and M categories had higher median pH than open water types. These wetlands frequently had anaerobic soils, as indicated by median redox values often less than 250 mV, the approximate point at which oxygen is fully depleted. The median for the most highly urbanized case was lower than for the N wetlands, which themselves had lower median redox than the M cases. Open water wetlands overall had higher redox readings than flow-through ones. This result is somewhat surprising, in that open water wetlands are thought to host more oxygenconsuming decomposition and to have oxygen replenished from the atmosphere less efficiently than flow-through cases. It was found in the synoptic study of 73 wetlands at the beginning of the program that open water zones had the lowest redox readings (less than 100 mV).16 Redox was below the level at which oxygen is generally depleted in the inlet, open water, and emergent zones, but not in the scrub-shrub

Urban Statusa & Morph N/OW

N/FT

All N

M/OW

M/FT

pH

Redox (mV).

TP (mg/kg)

TKN (mg/kg)

Org. (%)

Cu (mg/kg)

Pb (mg/kg)

Zn (mg/kg)

As (mg/kg)

Mean Maximum St. Dev. CV Median n Mean Maximum St. Dev. CV Median n Mean Maximum Std. Dev. CV Median n Mean Maximum St. Dev. CV Median n Mean Maximum St. Dev.

5.43 6.67 0.64 12% 5.40 47 5.73 7.12 0.48 8% 5.70 27 5.54 7.12 0.60 11% 5.60 74 5.31 6.72 0.90 17% 5.11 26 5.95 6.96 0.51

143 649 322 225% 153 46 113 629 296 262% 184 27 132 649 311 236% 184 73 317 656 227 72% 362 26 165 611 279

743 6579 1087 146% 251 55 839 8882 1698 202% 342 27 775 8882 1310 169% 283 82 1114 3827 1019 91% 945 25 756 2743 819

5261 27369 5983 114% 2866 58 3899 14223 3297 85% 3799 29 4807 27369 5261 109% 2885 87 6354 22517 5670 89% 5783 25 3999 27967 5942

45.5 97.3 34.2 75% 47.0 58 36.1 97.3 28.8 80% 34.1 29 42.4 97.3 32.6 77% 35.8 87 35.4 92.3 29.9 85% 23.7 25 25.7 92.3 28.1

58 2221 300 515% 16 54 21 40 13 61% 17 27 46 2221 245 536% 16 81 12 24 7 60% 14 28 18 63 12

65 418 96 147% 24 54 33 322 60 184% 18 27 54 418 87 159% 20 81 32 101 30 95% 21 28 77 530 89

27 154 29 106% 18 54 31 103 30 97% 17 27 28 154 29 103% 17 81 22 92 24 107% 15 28 60 334 62

6.5 20 5.4 84% 4.4 54 15 225 42 284% 6.6 27 9.3 225 25 267% 6.0 81 6.2 16 4.4 70% 4.8 28 8.1 25 5.2

61

Statistic


TABLE 2-5 Soil Quality Statistics for Wetlands Not Experiencing Significant Urbanization Change (1988–1995) Grouped by Urbanization and Morphology

Urban Statusa & Morph

All M

All OW

All FT

a

pH

Redox (mV).

TP (mg/kg)

TKN (mg/kg)

Org. (%)

Cu (mg/kg)

Pb (mg/kg)

Zn (mg/kg)

As (mg/kg)

CV Median n Mean Maximum Std. Dev. CV Median n Mean Maximum St. Dev. CV Median n Mean Maximum St. Dev. CV Median n Mean Maximum St. Dev. CV Median n

9% 6.09 45 5.71 6.96 0.74 13% 5.78 71 5.88 6.97 1.01 17% 6.46 32 5.39 6.72 0.74 14% 5.35 73 5.87 7.12 0.70 12% 5.92 104

169% 226 43 222 656 269 121% 306 69 87 640 291 335% 91 32 206 656 302 147% 305 72 127 640 286 226% 162 102

108% 481 41 892 3827 909 102% 537 66 654 2995 784 120% 314 34 859 6579 1074 125% 414 80 744 8882 1102 148% 378 102

149% 2021 43 4865 27967 5912 122% 2764 68 2703 11282 2892 107% 2033 36 5590 27369 5877 105% 3141 83 3540 27967 4449 126% 2274 108

109% 12.6 47 29.1 92.3 28.9 99% 15.1 72 31.6 80.9 26.3 83% 22.8 35 42.4 97.3 33.1 78% 34.2 83 30.3 97.3 27.8 92% 16.1 111

68% 17 43 16 63 11 69% 15 71 31 63 17 56% 30 32 43 2221 244 572% 15 82 23 63 15 67% 20 102

115% 57 43 59 530 75 126% 34 71 89 273 68 76% 64 32 54 418 81 151% 24 82 69 530 78 113% 46 102

104% 48 43 45 334 53 119% 33 71 103 456 112 109% 65 32 25 154 27 107% 16 82 66 456 80 123% 45 102

65% 7.7 43 7.3 25 5.0 68% 6.2 71 13 40 9.4 74% 10 32 6.4 20 5.1 80% 4.5 82 11 225 22 199% 7.70 102

See Table 2-1 for definitions of Urban Status abbreviations.


H/FT

Statistic

62

TABLE 2-5 (continued) Soil Quality Statistics for Wetlands Not Experiencing Significant Urbanization Change (1988–1995) Grouped by Urbanization and Morphology


63

and forested zones. In another contrast with the more recent results, soils in the inlet zones of wetlands in nonurban wetlands had significantly (p less than .05) lower redox than in urban wetlands. The highest median TP occurred in moderately urbanized wetlands, as did the highest median for TKN. The lowest median for TP was in the nonurban open water category whereas the lowest median for TKN was found among the highly urbanized flow through wetlands. The N urbanization category had median organic content over 30%, although with extensive variation. The M and H sites overall had about half to two-thirds of that level. On the whole, open water wetlands exceeded flow-through ones in organics. This finding is as expected, since ponded systems have more primary productivity and capability of settling solids. Soil texture is important to the nutrition, structure, drainage, and erosion prevention characteristics of a soil. Nutrients are found in a soil attached to organic matter, clay particles, and metal oxides (especially iron oxides). Soils with a high portion of clay, organic material, or both adsorb water and nutrients much more readily than soils low in these components. Fine-textured soils have a more compact structure, which may impede aeration of the soil. Clays adsorb water and if positioned lower down in the soil profile, can impede drainage, causing an impervious layer and creating a wetland. Sandy soils have very little cohesion and erode much more easily than silt- or clay-rich soils. One of the influences of urbanization on wetland ecosystems is deposition of sediments from development activities (clearing and grading). Table 2-6 presents a comparison of soil textures in 1989 and 1995 for the wetlands that did not experience significant watershed change. As was hypothesized for these cases, little change occurred over these years regardless of urbanization or morphological status. The soils of the majority of these wetlands were dominated by silt-range particles, again irrespective of status. One N/OW and one M/FT site, located in different parts of the study area, had predominately sand. With two exceptions, the wetlands were found to have relatively little clay (less than or equal to 20%). However, a wetland in north King County and one in south King County had about 30% and 50%, respectively. It bears noting that some of the samples contributing to these statistics had greater than 25% organic content, in the range where the analytical method is less accurate. Analysis of the PSD measurements within individual wetlands indicates that PSD often varied substantially across wetlands and showed no trends with the amount of organic matter in the soil or the soil series. No association was seen between the total suspended solids in the surface water and changes in soil texture. However, soils located near the inlets of M and H wetlands were significantly (p less than .05) more likely to have more sand than silt as compared to other locations. Metals in Soils Cadmium, lead, and zinc in wetland soils were observed to be highly variable from year to year, but copper and arsenic varied less. Overall, there was a declining trend in soil metal content over the years of the study. These results are somewhat sur-

64


TABLE 2-6 Comparison Changes in Average Particle Size Distributions from 1989 to 1995 in Wetlands that Experienced Little Urbanization Change Grouped by Urbanization and Morphological Classifications Site

Wetland Area (ha)

PSD 1989 (% sand/silt/clay)

PSD 1995 (% sand/silt/clay)

AL3 HC13 RR5 SR24

Nonurbanized Open Water (N/OW) 0.81 26/54/20 1.62 47/47/6 10.52 74/15/11 10.12 1/89/10

No data 45/37/18 68/21/11 6/75/19

LCR93 MGR36

Nonurbanized Flow Through (N/FT) 10.93 No data 2.23 13/76/11

30/50/20 20/70/10

ELS39 SC84 TC13

Moderately Urbanized Open Water (M/OW) 2.02 35/49/16 15/69/16 2.83 4/81/15 11/73/16 2.06 30/41/29 38/32/30

ELW1 FC1 SC4

Moderately Urbanized Flow Through (M/FT) 3.84 83/13/4 75/18/7 7.28 13/71/16 10/75/15 1.62 No data No data

B3I LPS9

Highly Urbanized Flow Through (H/FT) 1.98 31/62/7 24/61/15 7.69 30/16/54 32/20/48

prising since the soil cores were 15 cm deep, representing soil horizons that would be expected to maintain fairly stable metals concentrations from year to year. Figure 2-1 shows that median concentrations of As, Cu, Pb, and Zn for all of the program wetlands generally declined each year. It is possible that metals enter and depart from wetland soils more easily than previously believed, permitting a rapid change in results in response to changes in inputs from the watershed. Declining metals pollution from vehicles and dissipating pollutants from industrial air pollution point sources, such as the closed ASARCO smelter in Tacoma, could explain the general decline of soil metals since the start of the program. Cadmium was undetectable in the soils of most monitored wetlands, except in three that also had relatively high Pb. This result is consistent with the observation that metals often increase in tandem. Although the program detected substantial increases in Cd, Pb, and Zn at several wetlands between 1989 and 1990, it is significant that there are no apparent common characteristics among these wetlands. They represent differing hydrology, ecology, and levels of watershed development.18


65

Annual Mean Concentration (mg/kg)

60 Cu Pb Zv As

50 40 30 20 10 No data

No data

0 1988

1989

1990

1991

1992

1993

1994

1995

FIGURE 2-1 Annual mean metal concentrations for all wetland samples in each year.

It can be seen in reviewing the metals data in Table 2-5 that, like water quality and general soil characteristics, soil metals exhibited extensive variability. Again, too, medians were normally considerably less than means. It is further apparent in Table 2-5 that median metals concentrations increased from nonurban to moderately urbanized and increased again in highly urbanized wetlands, except for a small drop in Cu from N to M. Flow-through wetlands overall had higher median concentrations of all metals than did open water ones, although very marginally so for Cu. This tendency was again stronger for the moderately urbanized than the nonurbanized wetlands. For the most part, soils exhibited the same trend as water quality, with quantities considered to be pollutants higher in FT than in the OW wetlands. It was thought that water column contaminants might be lower in open water wetlands because of losses to the soil. However, this supposition was not borne out by the soil results. Having the two most developed sites in the FT group may be skewing the results. The Washington Department of Ecology set metals criteria for freshwater sediments in terms of lowest effect and severe effect thresholds.21 The criteria are

Copper Lead Zinc

Lowest Effect Threshold (mg/kg dry soil)

Severe Effect Threshold (mg/kg dry soil)

16 31 120

110 250 820

No mean or median value exceeded the severe effect criteria, and very few individual readings surpassed them at any time during the program. However, some Cu and Pb means and even medians exceeded lowest effect thresholds. Many

66


individual readings in wetlands in all urbanization categories were beyond these lower limits. Even though there is a trend toward increasing soil metals with urbanization, it is a fact that soil in either urban or nonurban wetlands can have elevated metals. These contaminants could be entering wetlands outside of urban areas in a variety of ways. Possibilities include via precipitation and atmospheric dryfall, dumping of metal trash, and leaching from old constructed embankments. Roads and narrowgauge railroad beds were built using mine tailings to serve logging operations in the last century, in the vicinity of some of the wetlands. This phenomenon suggests the need for site-specific inquiries into metals pollution in Pacific Northwest palustrine wetlands, rather than reliance on broad patterns.

SUMMARY OF SOIL CHARACTERISTICS OF WETLANDS WITH NONURBANIZED WATERSHEDS A soils portrait of Puget Sound Basin lowland palustrine wetlands relatively unaffected by humans shows a somewhat acidic condition; pH is very likely to be in the range of 5 to 6. With redox as a basis, soils at many times and places will be anaerobic, but with great variability. Phosphorus is likely to be somewhere in the vicinity of 300 mg/kg, with nitrogen (TKN) approximately an order of magnitude higher. Based on these results, most soil samples from nonurban wetlands can be expected to have greater than 25% organics, and greater than 10% is extremely likely. Texture appears to be more a function of local conditions than a function of urbanization, or lack of it. The metals As, Cu, Pb, and Zn can range over two orders of magnitude from a minimum in the low parts per million (mg/kg) region, in the soils of these nonurban wetlands. Most commonly, they appear to have approximately equal amounts of Cu, Pb, and Zn, around 20 mg/kg, and about one-quarter to one-third as much as As. This level and the observed variation around it are sufficiently high to exceed lowest threshold effect freshwater sediment criteria for Cu often and for Pb occasionally, but very rarely for Zn.

REFERENCES 1. Horner, R. R. and K. J. Raedeke, Guide for Wetland Mitigation Project Monitoring, Washington State Department of Transportation, Olympia, 1989. 2. Horner, R. R. and K. A. Ludwa, Monitoring and Quality Assurance/Quality Control Plan for Wetland Water Quality and Hydrology Monitoring, Center for Urban Water Resources Management, University of Washington, Seattle, 1993. 3. Reinelt, L. E. and R. R. Horner, Characterization of the Hydrology and Water Quality of Palustrine Wetlands Affected by Urban Stormwater, Engineering Professional Programs, University of Washington, Seattle, 1990. 4. King County Resource Planning Section, Puget Sound Wetlands and Stormwater Management Research Program: Initial Year of Comprehensive Research, Engineering Professional Programs, University of Washington, Seattle, 1988.


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5. Azous, A., An Analysis of Urbanization Effects on Wetland Biological Communities, M.S. thesis, University of Washington, Department of Civil Engineering, Seattle, 1991. 6. Reinelt, L. E. and R. R. Horner, Urban stormwater impacts on the hydrology and water quality of palustrine wetlands in the Puget Sound region, in Puget Sound Research ‘91 Proc., Seattle, WA, January 4–5, 1991, Puget Sound Water Quality Authority, Olympia, 1991, p. 33. 7. Platin, T. J., Wetland Amphibians Ambystoma gracile and Rana aurora as Bioindicators of Stress Associated with Watershed Urbanization, M. S. C. E. thesis, University of Washington, Department of Civil Engineering, Seattle, 1994. 8. Ludwa, K. A., Urbanization Effects on Palustrine Wetlands: Empirical Water Quality Models and Development of a Macroinvertebrate Community-Based Biological Index, M. S. C. E. thesis, University of Washington, Department of Civil Engineering, Seattle, 1994. 9. Taylor, B., K. A. Ludwa, and R. R. Horner, Urbanization effects on wetland hydrology and water quality, in Puget Sound Research ‘95 Proc., Seattle, January 12–14, 1995, Puget Sound Water Quality Authority, Olympia, 1995, p. 146. 10. Chin, N. T., Watershed Urbanization Effects on Palustrine Wetlands: A Study of the Hydrologic, Vegetative, and Amphibian Community Response During Eight Years, M. S. C. E. thesis, University of Washington, Department of Civil Engineering, Seattle, 1996. 11. Valentine, M., Assessing Trace Metal Enrichment in Puget Lowland Wetlands, Nonthesis paper for the M. S. E. degree, University of Washington, Department of Civil Engineering, Seattle, 1994. 12. Gilbert, R. O., Statistical Methods for Environmental Pollution Monitoring, Van Nostrand Reinhold, New York, 1987. 13. Mitsch, W. J. and J. G. Gosselink, Wetlands, 2nd ed., Van Nostrand Reinhold, New York, 1993. 14. Welch, E. B., Ecological Effects of Waste Water, Cambridge University Press, Cambridge, U.K., 1980. 15. Municipality of Metropolitan Seattle, Water Quality of Small Lakes and Streams, Western King County, 1990–1993, Seattle, 1994. 16. Horner, R. R., F. B. Gutermuth, L. L. Conquest, and A. W. Johnson, Urban stormwater and Puget Trough wetlands, in Proc., First Annu. Meet. Puget Sound Research, Seattle, March 18–19, 1988, Puget Sound Water Quality Authority, Seattle, 1988, p. 723. 17. Cooke, S. S., K. O. Richter, and R. R. Horner, Puget Sound Wetlands and Stormwater Management Research Program: Second Year of Comprehensive Research, Engineering Professional Programs, University of Washington, Seattle, 1989. 18. Richter, K. O., A. Azous, S. S. Cooke, R. Wisseman, and R. Horner, Effects of Stormwater Runoff on Wetland Zoology and Wetland Soils Characterization and Analysis, PSWSMRP, Seattle, 1991. 19. Cooke, S. S., The effects of urban stormwater on wetland vegetation and soils: a long-term ecosystem monitoring study, in Puget Sound Research ‘91: Proc., January 4–5, 1991, Seattle, WA, Puget Sound Water Quality Authority, Olympia, 1991, p. 43. 20. Cooke, S. S. and A. Azous, Characterization of Soils Found in Puget Lowland Wetlands, Engineering Professional Programs, University of Washington, Seattle, 1993. 21. Washington Department of Ecology, Summary Criteria and Guidelines for Contaminated Freshwater Sediments, Olympia, 1991.

3

Characterization of Central Puget Sound Basin Palustrine Wetland Vegetation Sarah S. Cooke and Amanda L. Azous

CONTENTS Introduction..............................................................................................................69 Methods....................................................................................................................70 Results......................................................................................................................72 Community Structure and Composition.........................................................72 Habitat Character ............................................................................................72 Wetland Plant Associations ............................................................................72 Abundance and Distribution of Invasive Plant Species .................................72 Community Richness......................................................................................75 Hydrologic Regimes by Habitat Type............................................................78 Hydrologic Regimes of Some Species...........................................................79 Discussion ................................................................................................................86 Acknowledgments....................................................................................................88 References................................................................................................................88 Appendix A: List of Plant Species and Frequency Found Among 19 Central Puget Sound Basin Palustrine Wetlands .................................................................90

INTRODUCTION Nineteen wetlands in the Central Puget Sound Basin in King County, Washington were studied for five years between 1988 and 1995. An additional seven wetlands were involved in special studies within the same period. The wetlands surveyed were inland palustrine wetlands ranging in elevation from 50 to 100 m above mean sea level and characterized by a mix of aquatic bed, emergent, scrub-shrub, and forested wetland habitat classes. Our purpose was to understand the richness, composition, and structure of wetland plant communities. In later years, defining hydrologic conditions for habitats and species also became a study focus. Changes to plant communities observed during the study are explored later, in Chapter 10. 1-56670-386-7/01/$0.00+$.50 © 2001 by CRC Press LLC

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70


Plant community structure for all the years was examined through analysis of species richness, composition, and percent cover. Ordination and classification analyses were used to identify distinct plant communities and to examine relationships between presence, abundance, and distribution of invasive species. Relationships between species presence, habitat structure, and hydrologic conditions are discussed.

METHODS Wetland sizes were estimated through analysis of U.S. Geographic System (USGS) 7.5-minute-series topographic maps and ranged from 0.4 to 12.4 ha. Plant communities in each wetland were characterized during a two- to three-week period in the growing season between July and August, for the years 1988, 1989, 1990, 1993, and 1995. Plant community composition and percentage cover were sampled in permanent plots adjacent to linear transects established across the hydrologic gradients of each wetland. Species cover was recorded using a cover class system based on the Octave Scale.1,2 Detailed protocols for the vegetation fieldwork are documented elsewhere.3 The data set also includes seven additional wetlands that were surveyed during the years 1993, 1994, and 1995 as part of related studies. Species were identified using the method of Hitchcock et al. and were verified with specimens from the University of Washington Herbarium.4 The Cowardin classification system was used to assign each sample plot a habitat category based on the dominant structure of the vegetation community, such as aquatic bed (PAB), emergent (PEM), scrub-shrub (PSS), forested (PFO), upland, or some transition zone between them (e.g., PEM/PSS).5 The Cowardin classification system was selected because it is widely used in functional assessments, wetland protection regulations, and mitigation criteria.6 In some cases the vegetation community class changed over time within sample plots and plots were recategorized as required. Sample plots in upland habitats were included in the documentation of plant species observed but were not included in analyses of wetland richness. Plants species in the sample plots were surveyed and the data used to calculate the frequency of species presence among the wetlands studied. Plant species presence was sampled in permanent plots established every 50 m along a gradient from the upland through the transition zones and, at intervals, crossing the different wetland vegetation communities. Total plant species richness was calculated for individual wetlands and for different habitat categories. Species were also tabulated according to wetland indicator status (whether obligate [OBL], facultative wetland [FACW], facultative [FAC], or facultative upland [FACU]) and according to form (e.g. grass, herb, shrub, or tree).7, 8 Vegetation community types were defined and described using ordination (DECORANA) and classification (TWINSPAN) comparisons.9,10 Plant community data were tabulated in a two-way matrix (species by cover) and were classified by grouping similar vegetation units into categories.11,12 All species in the sample stations were included. Ordination was used to graphically display the species groups showing similar communities plotted close together and dissimilar communities plotted further apart.2,10 The frequency of species and the relative dominance of

Characterization of Central Puget Sound Basin Palustrine Wetland Vegetation 71

species were both described by the proportion of vegetation sampling plots in which the species were found. The year was divided into four seasonal periods important to plant growth, an early growing season, defined to be from March 1 through May 15, an intermediate growing season which lasts from May 16 to August 31, senescence lasting from September 1 to November 15th, and dormancy and decay, November 16 to February 28. The seasonal hydrologic regime was calculated for each vegetation sample station from 1988 to 1995. Species found in each sample station were associated with the seasonal hydrologic regime observed at the station. These data were used to describe a hydrograph for many commonly found wetland plants showing conditions for instantaneous (labeled “instant” on the graphs) and maximum water depths. The association is based on plant species presence indicating conditions favorable to species survival. Hydrologic measurements included instantaneous water levels from staff gauges for measuring typical water depths found during monitoring visits, and peak levels from crest gauges to measure depths from storm events occurring between monitoring visits. These were recorded at least eight times annually (measured every four to six weeks) while water was present in the wetlands.13 Typical (instantaneous) and maximum water depths were averaged for each season and year. Water level fluctuation (WLF) was calculated as the difference between the maximum depth and the average of the current and previous instantaneous water depths for each four- to six-week monitoring period. Mean WLF was calculated by averaging all WLFs for a given season or year (see Chapter 1, for the equation used). Habitats within individual wetlands were surveyed to determine the elevation of the plant community in relation to the hydrologic monitoring location. The elevation of all vegetation-sampling stations relative to the water depth measured at the wetland gauge was used to determine the likely water depths at the vegetation sample stations during each season. The calculation was based on the assumption that water depth measured at the monitoring station would, when corrected for elevation, accurately reflect the hydrologic conditions found throughout the wetland. This was not always true as hydrologic conditions in and around the vegetation stations sometimes varied from the conditions predicted through elevation change alone. Sometimes intervening topography or large woody debris would produce localized impoundments or dry hummocks unaccounted for in the calculation. Whenever such plots were identified more accurate surveys were made or plots were eliminated from the analysis. In addition, hydrologic measurements did not tell us whether soils were dry or saturated so field observations augmented the analysis. Negative numbers in the bar chart hydrographs are to be read as below the water surface, or inundated. Positive numbers represent the distance, in elevation, above the water surface and indicate the plant or community being examined is dry during that period. Negative numbers are interpreted as depth of inundation. Bar charts show the median and the central 80% of the range of observations for the condition being evaluated. The solid portion of the bar represents the central 50% of observations. Outliers are not shown in order to illustrate the most likely range of wettest to driest conditions where particular wetland habitats or species would be found.

72


RESULTS COMMUNITY STRUCTURE

AND

COMPOSITION

We identified 242 plant species in 26 wetlands over the study period (a complete list of species and their occurrence is provided in Appendix A to this chapter). Of these 242 different species, most were herbs (46%), followed by shrubs (23%), grasses (10%), and trees (7%). Other species identified included ferns and horsetails (6%), sedges (6%), and rushes (2%); 65 species were obligate (27%), 56 were FACU (23%), 55 FAC (23%), and 38 FACW (16%) species; 29 (12%) species had no indicator status at the time of the study. There were 45 species (19%) found in only one (4%) of the 26 wetlands surveyed. Over 38% of plant species were found in less than three wetlands (12%). The distribution of plants by indicator status was similar to the distribution of species: 40% of obligate, 35% of FAC, and 39% of FACU species were also found in three or fewer wetlands. FACW species, on the other hand, were generally more widely dispersed among wetlands, with all species observed in at least eight wetlands (31%). Polystichum munitum, Rubus spectabilis, and Rubus ursinus were observed in all 26 wetlands but were usually low in number. Spirea douglasii was among the most dominant species, occurring in 96% of wetlands (25 of 26) and dominating coverage in 21% of locations where it was observed. Alnus rubra, Athyrium filixfemina, and Salix scouleriana were also found in 25 of 26 wetlands but were less dominant in coverage. Most of the widely distributed species were facultative and facultative upland species. Widely dispersed wetland species in addition to Douglas spirea included Epilobium ciliatum (Watson willowherb) (FACW) and Lysichitum americanum (skunk cabbage) (OBL). Phalaris arundinacea (reed canarygrass), a locally invasive noxious weed, was observed in 69% of wetlands (18 out of 26) and dominated 19% of observed locations. Other locally common and dominant wetland species included Ranunculus repens (creeping buttercup) found in 65% (17) of wetlands, and Juncus effusus (soft rush), observed in 58% (15) of the wetlands. Fortunately, Lythrum salicaria (purple loosestrife), a formidable noxious weed, was observed in only one wetland. Table 3-1 shows some of the most common and least common plants categorized by occurrence and cover dominance.

HABITAT CHARACTER Habitats identified in the 26 wetlands include the four Cowardin categories of aquatic bed (PAB), emergent (PEM), scrub-shrub (PSS), and forested (PFO), an additional two habitats called BOG and UPL (upland transition), and combinations indicating transitions between habitats. Plant communities of different habitats were evaluated with respect to the dominant plants and their associated wetland indicator status. These distributions are shown in Table 3-2. The table shows that obligate and FACW species dominate PAB and PEM habitats. PSS habitats were more evenly distributed and PFO and upland habitats were dominated by FAC and FACU species. A limited number of bog habitats were also sampled and were predominantly obligate and FACW species.

Characterization of Central Puget Sound Basin Palustrine Wetland Vegetation 73

TABLE 3-1 Species Occurrence for Different Categories of Plant Type and Cover Dominance Cover Dominance Category

High Occurrence (>80% wetlands)

Low Occurrence (

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